IN CARMEL SUBMARINE CANYON, CALIFORNIA: ASPECTS OF FISHERIES AND HABITAT ASSOCIATIONS

Transcription

1 THE SPOT PRAWN (Panda/s platyceras Brandt 1851) RESOURCE IN CARMEL SUBMARINE CANYON, CALIFORNIA: ASPECTS OF FISHERIES AND HABITAT ASSOCIATIONS A Thesis Presented to the Faclty of California State University, Stanislas throgh Moss Landing Marine Laboratories In Partial Flfillment of the Reqirements for the Degree Master of Science in Marine Science By Kyra Layne Schlining I 999 May 1999

2 Unpblished Work Copyright 1999 Kyra Layne Schlining 111

3 ACICNOWLEDGEMENTS As with many MLML theses, this project was an enormos effort that wold not have been possible withot the incredible amont of spport I received from a wide variety of mentors, colleages, family, and friends. I wold like to start by thanking my advisors James Nybakken, Jdith Connor, Pamela Roe, and Mary Yoklavich for their constrctive criticism. Mary was the spark that ignited this research project and I want to thank her for her great inspiration and carefl attention to details. I owe a vast debt of gratitde to Jerry Spratt, of the California Department of Fish and Game, for initiating me into the wonderfi!l world of fisheries and for being a dedicated editor for the fisheries chapter of my research. Hge thanks to.jeff "Iron Stomach" Field who proved himself qintessential dring field sampling in rogh seas. Caren Braby, Karen Giver, George Matsmoto, Kevin Raskoff, and Kris Rodgers Walz all contribted invalable inpt on figres and editorial advice. Thanks to Se Service, Rob Sherlock, Jeff Field, and Jonathan Geller for providing essential advice on statistical analyses. And thanks to Dan Davis for explaining problems with perspective. Others who provided inpt and/or spport inclde Karen Light, Se Lisin, and Chris Harrold, of the Monterey Bay Aqarim, Gail Johnston, Sandy Yarborogh, and Joan Parker, ofmlml, Bob. Leos, Deidre Sllivan, Lynn Laermann, Rhoda Lin, and Nancy Jacobsen-Stot. IV

4 I am very gratefl for financial spport from the Monterey Bay Aqarim Research Institte, the California Department of Fish and Game, the Earl and Ethel Myers Oceanographic Trst, and the David and Lcile Packard Fondation. A special thank yo to the Aliotti family of commercial prawn trappers for their gracios cooperation, and also to Tim Marasich for his "view from a fisher". Thanks to my family and friends for continal encoragement throgh the years. And lastly, I am tremendosly gratefl for the spport of my hsband, Brian, who helped me every step of the way. v

5 TABLE OF CONTENTS PAGE Acknowledgements... List of Tables... List of Figres List of Appendices... Abstract... General Introdction... 1v vii viii x x1 I Spot Prawn Fishery... 3 Introdction Methods... 7 Reslts... 1 Discssion Depth and Habitat Associations Introdction Methods Reslts Discssion General Conclsions Literatre Cited Tables Figres Appendix VI

6 LIST OFT ABLES TABLE PAGE 1. Statistical reslts for catch-per-nit-effort (CPUE in kilograms per trap), male to female sex ratios, and carapace lengths (mm) for male, transitional, and female spot prawns, close to and far away from, inside and otside of the Carmel Bay Ecological Reserve, California, and for verss Mean carapace lengths (mm) for spot prawns from the present stdy Compared to past observations on spot prawn carapace lengths in the California area Sbstratm morphology classification system sed for DSRV Delta sbmersible video transects in Carmel Canyon, California Abndance of spot prawns (P) and galatheid crabs (G) in Carmel Canyon DSRV Delta sbmersible transects shown by depth VII

7 LIST OF FIGURES FIGURE PAGE 1. Monterey area spot prawn landings by gear (kilograms x 1) and catch-per-nit-effort (CPUE in kilograms per trap) for the Carmel Canyon trap fishery from Map of Carmel Canyon, California. Area east of the line connecting Pescadero Point and Granite Point encompasses the Carmel Bay Ecological Reserve Catch-per-nit-effort (CPUE in kilograms per trap) for inside the Carmel Bay Ecological Reserve and two locations otside the reserve, one close to the bondary and one far from the reserve, compared to the annal mean from Sex ratios for spot prawns otside and inside of the Carmel Bay Ecological Reserve, California Freqency distribtion of carapace lengths (mm) for male, transitional, and female spot prawns otside and inside of the Carmel Bay Ecological Reserve, California Freqency distribtion of carapace lengths (mm) for male, transitional, and female spot prawns from the Carmel Canyon trap fishery (December 1967 to March 1968 and December 1996 to March 1997) Percent gravid female spot prawns from Carmel Canyon trap fishery, shown by month (Jly 1996 to Jne 1997) Map ofdsrv Delta video transect locations in Carmel Canyon, California Density (nmber m') at five depth intervals for spot prawns from 21 video transects condcted from the DSRV Delta in Carmel Canyon, California Percent occrrence of available habitat type and spot prawn density (nmber m- 2 ) in Carmel Canyon from 21 DSRV Delta transects II. Percent occrrence of available habitat type and spot prawn density (nmber m 2) in Carmel Canyon from 21 DSRV Delta transects shown at: a) 1m, b)!5 m, c) 2m, d) 25m, and e) 3m... 5 Vlll

8 FIGURE PAGE 12. Map of prawn sightings in Monterey Bay for benthic ROY Ventmw video footage from Prawn conts per depth for benthic ROY Ventana video footage from Percent prawn occrr-ence per habitat type for benthic ROY Ventana video footage at for depth intervals IX

9 LIST OF APPENDICES APPENDIX PAGE A. Transect nmber, transect depth (m), sbmersible speed (em s 1 ), and length traversed (m) for all DSRV Delta transects in Carmel Canyon X

10 ABSTRACT Observations were made on spot prawns (Panda/s platyceras) inside and otside of a small marine protected area, the Carmel Bay Ecological Reserve, in order to qantify the effectiveness of the reserve in enhancing this commercial resorce. I compared catch-pernit-effort (CPUE), sizes, and sex ratios inside and otside of the reserve from Jly 1996 to Jne I also compared the prawn sizes observed dring this stdy to sizes observed dring sampling by the California Department offish and Game in The reslts indicate that there were significant differences in CPUE, sizes, and sexes inside and otside of the reserve as well as between past and present sampling periods. Most notably the CPUE was significantly greater inside compared to otside of the reserve and also greater close to (bt otside) the reserve compared to far from the reserve. These reslts spport crrent theories on the vale of marine reserves for protecting resorce biomass and potentially fortifying adjacent fisheries throgh adlt emigration. For the second part of this stdy, I analyzed spot prawn habitat associations in the same area (Carmel sbmarine canyon) sing in sit videotaped images. I also noted macroorganisms commonly associated with spot prawns in these areas. The reslts indicate that spot prawns are actively selecting habitats that are complex mixes of sediment and varios sizes of consolidated sbstrata. The highest prawn density for a habitat patch was 2.6 m- 2 on a steeply sloping sediment and gravel bottom at a depth of 2m on the north wall of the canyon. Spot prawns were fond to be commonly associated with galatheid crabs and piles of drift algae fond in the canyon axis. XI

11 GENERAL INTRODUCTION Spot prawns, Panda/s platyceras (Brandt, 1851 ), are caridean shrimp fond from Unalaska, Alaska to San Diego, California, and also off the coast of Japan (Btler, 1964). Commonly known as spot prawns de to a pair of white spots on the first and fifth abdominal segments, they are the largest shrimp fond off the North Pacific coast (Btler, 1964; Barr, 1973). Spot prawns are fond in rocky marine benthic areas in water depths from m (Btler, 197). The jveniles are fond in shallow-water bays and inlets where they feed on detrits and small crstaceans, and migrate to deeper regions as they matre (Btler, 1964; Balsiger, 1979; Snada, 1984). The adlt prawns are nonspecialized predators and scavengers, and may feed on other shrimp, plankton, small mollscs, worms, sponges, and dead tish (Snada & Richards, 1992). While die! vertical migration has been demonstrated in several species of pandalids, spot prawns are benthic foragers dring both day and night (Snada & Richards, 1992). Spot prawns are preyed pon by a wide variety of carnivores, inclding hmans, most large fish, birds, seals, octopses, and crabs (Balsiger, 1979; California Department offish & Game, 1995). As with many other pandalids, spot prawns are protandric hermaphrodites, and spend their first three years as males. After spawning as males, they transform into females and can potentially spawn for one or two more years (Rensel & Prentice, 1978). Spawning takes place in September, and the females carry the eggs ntil they hatch into zoea larvae, sally no later than April (Snada & Richards, 1992). Off the California coast spot prawns live p to six years and reach a maximm carapace length (CL) of 63 mm and a I

12 2 maximm total length of3 ern (Btler, 1964; Barr, 1973, Balsiger, 1979; Snada, 1986). In contrast, the same species fond off the coast of British Colmbia, Canada, lives to only for years and grows to a maximm CL of 4 mm (Btler, 1964). The overall objectives of my stdy were to a) evalate whether spot prawns from the trap fishery adjacent to the Carmel Bay Ecological Reserve exhibit significant differences in sizes, sex ratios, or abndance inside verss otside of this no-take reserve, and b) determine patterns in spatial distribtion and habitat se by spot prawns in the Carmel sbmarine canyon, sing qantitative video transects.

13 SPOT PRAWN FISHERY Introdction Cal(f'omia jishe1y The California spot prawn fishery originated dring the 193s when fishers from the port of Monterey began landing spot prawns taken incidentally in octops traps (Snada & Richards, 1992). Sbstantial landings of the spot prawn are a relatively recent development off the California coast, with approximately 9 kg landed per year p to the early 197s (Balsiger, 1979; Snada & Richards, 1992). In 1974, there was a large increase in spot prawn landings, with 83, kg caght in trawls off Santa Barbara, which sparked a growing interest in this fishery (Balsiger, 1979; Snada & Richards, 1992). Spot prawn catches reached 168, kg in 1981, with most prawns caght in trawls off Santa Barbara (Snada & Richards, 1992). Landings declined to 23, kg in 1984 when a closed season for the trawlers was imposed by the California Fish and Game Commission (Snada & Richards, 1992). Shortly thereafter trapping became poplar becase trapped animals were landed alive and fetched a mch higher price per pond than trawled prawns that were generally landed dead (Snada & Richards, 1992). By 199 statewide landings were over 141, kg, with most landings corning from traps (Snada & Richards, 1992). Landings contined to increase and in 1997 they exceeded 34, kg, with a vale of nearly $5 million, of which the majority were landed in sothern California (California Department of Fish & Game, 1998). Recently, new restrictions have been established for the spot prawn fishery in several fishing zones in sothern California in order to avoid 3

14 overfishing, which reslted in the near collapse over the past 1 to 15 years of the spot 4 prawn fishery in Alaska and Washington (Calfornia Department offish & Game, 1995). Monterey Bay jishe1y Spot prawns spport a modest commercial fishery in the central California area arond Montery Bay. Crrently, there are five local vessels that trap prawns in Carmel Canyon (jst soth of Monterey Bay), and 8-13 vessels that trawl for them between Morro Bay and Pt. Reyes (J. Spratt, California Department offish & Game, Monterey Unit, pers. comm.). Prawns caght in traps mainly spply Monterey restarants and markets. The limitations on the spot prawn fisheries in the Monterey Bay area inclde a maximm limit of 1 ponds of bycatch in trawls; gear restrictions, sch as maximm sizes for traps and trap openings, and minimm trawl mesh sizes; and traps mst be eqipped with an approved self-destrcting device in the event that they are lost at sea (California Department offish & Game, 1995). Spot prawn landings for the Monterey area ranged between 4-15 kg per year ntil the late 196's when landings increased an order of magnitde to 4-9 kg per year. They remained at that level ntil the early 199s (California Department of Fish & Game, 1995). Prawn trawlers from otside regions entered the Monterey prawn fishery in 1994, and landings increased dramatically to a record of31,746 kg (J. Spratt, pers. comm.). Combined trap and trawl landings remain high, crrently between 12,-32, kg per year (Figre I). As a reslt of this recent activity the spot prawn fishery has become one of the most valable fisheries in the Monterey area, commanding an ex-vessel

15 price of $16.5 per kg and bringing in a total vale of $5, in 1997 (California 5 Department offish & Game, 1998). The Monterey branch of the California Department of Fish and Game has docmented catch-per-nit-effort (CPUE), nmber of vessels fishing, and method and location of captre from 1978 to the present. This large database provides valable information on trends in this fishery. Poplations of shrimp ndergo large flctations in nmber over a cycle of a few years, and it is nknown whether these flctations are cased by natral events, by hman impact, or by a combination of these two factors (Balsiger, 1979; Snada & Richards, 1992). Management of many commercial fisheries is based on the optimm sstainable yield, which is the maximm sstainable yield (the greatest amont of the resorce that can be exploited withot depleting the stocks over time) modified by relevant ecological, economic or social factors (Wieland, 1992; Speer eta!., 1997). Poplation parameters necessary to formlate these management models for deep water organisms, sch as natral mortality, age determination and growth rates, stock identification, and the origin of recritment with regard to larval distribtion, remain largely nknown de to the difficlty and expense of sampling (Balsiger, 1979). There has been concern expressed by both the prawn trappers and the California Department of Fish and Game regarding the recent expansion of the t!shery and the nknown impact the increased trawl catches may have on the spot prawn resorce in the area. The relationship between the Monterey Canyon and the Carmel Canyon spot prawn stocks is nclear. Information on the stats of the prawn resorce is essential before poplation models and optimm yield can be determined.

16 Stdy area 6 Carmel Canyon is located off the coast of central California, soth of Monterey Bay (Figre 2). The head of the canyon, at a depth of 1 m, is within.4 km of shore and has been a prime spot prawn fishing target for many years. The California Fish and Game Commission established the Carmel Bay Ecological Reserve (CBER) on Febrary 2, 1976, marking the beginning a very controversial closre of the head of the canyon to commercial prawn fishing (California Fish & Game Commission, 1976). The prawn fishers believed that trapping wold be allowed within the proposed reserve, bt when the paperwork was finalized, trapping was exclded as well as all other comercial fishing (Aliotti, prawn trap fisher, Monterey, pers. comm). The CBER is demarcated simply by a line-of-sight from Pescadero Point (121 57'"W 36 33'36"N) to Granite Point (12l 56'24"W 36 31'12"N) (Figre 2). The park rangers patrolling nearby Point Lobos Ecological Reserve reliably report nathorized boats entering the CBER which, along with the pblished reglations, has kept the area virtally nfished for the past 22 years. The area jst otside the CBER is relatively heavily fished, as there is a tendency to "fish the line" marking the reserve (Bohnsack, 1993; J. Spratt, pers. comm.; K. Schlining, pers. obs.). Until the present stdy, the effectiveness of this reserve had never been evalated relative to resorce management. Objectives De to the recent growth in the central California spot prawn fishery and the pacity of data on the local resorce, the California Department offish and Game, in

17 cooperation with Moss Landing Marine Laboratories, initiated a program to collect 7 detailed biological and fishery information on the spot prawn, beginning with the Carmel Canyon trap fishery. The objectives of my stdy were to a) determine the importance of the Carmel Bay Ecological Reserve relative to the spot prawn resorce in central California by investigating prawn catch, sizes, and sex ratios inside and otside of the reserve, and b) to assess changes in the catch and size of the resorce over the past 2-3 years. Materials and Methods Sampling procedre Data on spot prawns were collected from the commercial prawn trap fishery dring thirty one-day trips to sea from Jly 1996 to Jne Catches were observed once a week, weather permitting, from for local vessels, all approximately m in length. In addition to normal fishing activities, these commercial prawn vessels were permitted to place two lines of traps inside the Carmel Bay Ecological Reserve once a month in order to make comparisons inside and otside the reserve. A typical commercial spot prawn trap is rectanglar, constrcted of 6-mm steelreinforcing bar covered with 37-rnm mesh netting, and has otside dimensions of.4 m x.4 m x I m. The traps are fished in lines, with 1-12 traps tied to a main line, and roghly 2 m between each trap. Each line is anchored at one end and has several floats marked with boat identification attached to the other. When the trap line is set, the anchor is placed at a depth of 2 to 3 m and the traps are dropped over the edge of the

18 8 sbmarine canyon wall. Traps hang down the canyon wall and tish at depths between 2 and 4 m. Fishers on each vessel generally set tive to ten lines of traps each day. Fetid fish carcasses from local fish processing companies are the primary bait. Traps are plled every 24 hors, emptied, rebaited, and reset immediately. The location and depth for each line of traps were recorded when the anchor was released over the side of the vessel side with a Global Positioning System (GPS) and a depth sonder. Biological data Biological data on prawn weight, size, and sex were collected on board the fishing vessels dring active operations. The variance in the nmber of prawns collected between lines (mean sqare error= 134) was far greater than the variance between traps (mean sqare error= 3) and traps on a line were not independent; therefore, all traps on one line were combined as one sample. After incidental species were removed, each sample of prawns (one line) was weighed to the nearest.1 kg. Individal prawns were not weighed de to problems of resolving small weights accrately on a moving vessel. Catch-per-niteffort (CPUE) was calclated for each line by dividing the total weight of the catch per line by total nmber of traps per line to prodce an average weight of catch per trap (in kilograms). A Mann-Whitney U-test was sed to compare the median CPUE from the 26 lines collected within the reserve to 26 lines from each of two locations otside the reserve, one close (.5-2. km) to the reserve bondary and one far ( km) from the reserve bondary (Zar, 1974). When the catch was small(< 5 prawns per line), all prawns were processed, bt when the catch was large (>5 prawns per line), a sbsample of 1-2 kg (approximately 3

19 prawns) was taken from each line for fiirther assessment of size and sex. Sizes were 9 measred to the nearest millimeter sing carapace length (CL), fi om the base of the eyestalk to the posterior mid-dorsal edge of the carapace. Difference in size was evalnated between the 26 stations close to the reserve and 26 far from the reserve, as well as, differences within and close to the reserve for male, female, and transitional prawns. Size was compared with at-test when assmptions of normality and homoscedasticity were met and with a Mann-Whitney U-test when assmptions were violated (Zar, 1974). Sex was determined by examining the second pleopod for the presence of the appendix masclina, a characteristic present in male prawns, or for the presence of the appendix intema, present in female prawns. Transitional prawns, in the process of changing from male to female, exhibit both strctres in a greatly redced fonn (see Figre 3-2 in California Department offish & Game, 1995). The male-to-female sex ratios were analyzed for significant differences inside and otside of the reserve sing a Pearson X 2 -test. Gravid females were also noted. Historical data From December 1967 to March 1968 the California Department offish and Game sampled spot prawns landed at Monterey. These measrements were taken dockside after the vessels were nloaded, while the present stdy was condcted at sea. Difference in size was analyzed between these data from December 1967 throgh March 1968 and my data from the same months in (Mann-Whitney U-test). For comparison, prawn sizes are also reported from data gathered by Dahlstrom from Janary 17 to Febrary 7 in Carmel Canyon, California (Dabstrom, 1963).

20 1 Access to fishing activity logs containing information on catch, nmber of traps, and catch location from 1978 to the present, was made available throgh the California Department offish and Game ( fishing activity logs, npblished data). From this information trends in CPUE were examined over nearly 2 years. Mean monthly CPUE from these historical logs were compared to mean monthly CPUE observed inside and otside the reserve dring this stdy, inclding both close and far locations. Reslts The median CPUE (kg per trap) close to the reserve was significantly greater than the median CPUE from the samples frther away from the reserve (Mann-Whitney U = 448.5, p <.43, Table 1). The median CPUE within the reserve was significantly greater than the median CPUE close to the reserve (U = 476., p <.12, Table 1). However, the mean CPUE from both otside reserve locations (close =.43 kg per trap, and far =.32 kg per trap) compares favorably with the mean annal CPUE over the past 2 years (.46 kg per trap) (Figre 3). The 78 lines sampled yielded 2749 prawns total, 114 prawns from locations close to the reserve bondary, 766 prawns from far away from the reserve, and 879 prawns from inside. For the males, carapace length (CL) was significantly larger far from the reserve (mean= 37.9 mm), than close to reserve (mean= 35.1 mm) (U = , p <. I, Table 1 ). Size of males was also significantly larger close to the reserve than inside the reserve (mean= 34. mm) (t = , p <. I, Table I). On the contrary, for the females, CL was significantly smaller far from the reserve (mean= 47.8 mm), when

21 11 compared to close to the reserve (mean= 48.8 mm) (U = , p =.2). There were no significant differences in size of female prawns between locations close to the reserve and inside the reserve (mean= 49.2 mm) (t = 1.34, p =.181 ). Size of transitional prawns was signi±"icantly larger far from the reserve (mean= 44.7 mm) when compared to size close to the reserve (mean= 41. mm) (U = , p <.1), bt significantly larger inside the reserve (mean= 43.4 mm) than close to the reserve ( U = 2147., p =.5). Size was not related to depth of anchor (inside reserve R 2 ;.12, otside reserve R 2 =.1) therefore, I did not inclde depth as a factor when looking at differences in size inside and otside of the reserve There was a significant difference in the sex ratios of prawns from inside compared to otside the reserve, with a larger nmber of males to females located inside ct. I = 7.85, p =.8, Table I). The ratio of males to females within the reserve was 2: 1 compared to an otside reserve ratio of 1.6: I (Figre 4). Smaller male sizes and larger female sizes were observed inside the reserve when compared to size freqency distribtions for prawns otside of the reserve (Figres 5). Male and female prawns were fond to be significantly smaller in the samples (mean CL = 37.9 mm and 47.8 mm, respectively) than those sampled in , (mean CL = 39. mm and 5.2 mm, respectively) with a U-vale for median male size of , and a U-vale for median female size of (p <.1 for both, Table 1, Figre 6). However, the transitional CLs were not significantly different from their conterparts (mean= 44.1 mm for both) with at-vale of (p =.87). Overall CLs in this stdy were similar to sizes measred by Dahlstrom (1963) for

22 all sexes (Table 2). The majority (6-9%) of female prawns were gravid from September 1996 throgh March 1997 (Figre 7). 12 Discssion The significantly larger catch-per-nit-effort observed within the Carmel Bay Ecological Reserve compared to both otside locations is one indication that the reserve may indeed be fnctioning for the benefit of the spot prawn resorce. There are nmeros ways reserves can potentially operate to protect and benefit harvested species, sch as by protecting spawning stock biomass, providing recrits to replenish fisheries, enhancing catches in adjacent fished areas throgh adlt emigration (spillover), protecting genetic diversity, and simply protecting habitat diversity (Bohnsack, 199; Roberts & Polnin, 1991; Roberts & Polnin, 1993; Rowley, 1994). The greatly elevated CPUE and the larger female prawn sizes within and close to the reserve indicate that the CBER may serve a role in protecting spa wing stock biomass. Frthermore, reserve spillover may be responsible for spporting the high CPUE close to the bondary of the reserve. Conversely, the gradient in CPUE from far to close to inside the reserve cold simply be indced by environmental factors changing with distance offshore, and not reserve effects. If this were the case, one wold expect to see similar size trends for all sexes of prawns. However, carapace lengths were significantly smaller inside the reserve for the male prawns, while the trend was in the opposite direction, althogh not significant, for female lengths, and lengths were significantly smaller for transitionals close to the reserve than for either inside or far locations. These patterns sggests an nderlying

23 distribtion mechanism more complex than simply a nearshore to offshore gradient of 13 ntrients or other physical factors sch as temperatre and salinity. There was a significant difference in sex ratio noted inside and otside the reserve. According to Snada (1986), a typical nfished hermaphroditic poplation is expected to exhibit a male to female ratio of at least 2: I. The male to female sex ratio observed within the reserve was as expected (2: 1) bt mch lower otside ( 1.6: I). Prawns have been shown to alter their sex ratios in response to environmental inflences (Charnov et al., 1978), and one can easily project potential complications arising from a poplation attempting to balance an insfficient ratio of males to females ensing from commercial fishing pressres. For example, there cold be a time delay for males beginning the transitional phase reslting in a sbseqent lower nmbers of females and eventally a decline in the poplation overall. In this sitation, one wold expect to see larger male sizes which was indeed the case otside of the reserve. Fishers in California have expressed reservations regarding the need for seqential seasonal closres for trawlers and trappers dring the ovigeros season for spot prawns. There is crrently a closre for trawlers in sothern California from November l to Janary 31, and an additional closre for trappers from Janary 16 to March 31 is being proposed in order to relieve fishing pressre dring this sensitive time of year (California Department offish & Game, 1995). The fishers contend that sch closres are prposeless as the prawns are gravid all year long. However, or gravid peaks correspond almost exactly to what was noted by Snada (1986) and are similar to peaks observed by

24 Btler (1964) off the coast of British Colmbia, Canada. These findings spport the 14 effectiveness of a seasonal closre as a sefl management tool. Carapace lengths from this stdy are smaller by a few millimeters for male and female prawns than for prawns measred 3 years ago. Shrinking mean sizes typically indicate a gradal decrease in poplation fitness that has been attribted to overexploitation (Bohnsack, 1993). Overfishing can enhance selection for individals that matre earlier, have a shorter life span, and a smaller adlt size (Bohnsack, 199; Bohnsack, 1993). However, it is impossible to make these kinds of inferences from two snapshots in time withot data collected in between. Longer term sampling mst be condcted to clarify possible trends. Sizes were not significantly smaller for the transitional prawns, and sizes were comparable to what has been previosly reported for this area by Dahlstrom (1963). Althogh it is clear that the spot prawn resorce is benefitting from the Carmel Bay Ecological Reserve, it is difficlt to qantify these effects. From this stdy I sggest that the reserve cold be acting as a harvest refge for the smaller male and the larger female prawns. Ftre stdies shold focs on looking for evidence of jvenile prawns in the shallower areas of Carmel Canyon. If the jveniles are sing the shallows of the CBER as a nrsery grond, as I sspect they may be, it wold add frther confirmation that the reserve is working toward the benefit of the resorce. The bondary for the Carmel Bay Ecological Reserve is an arbitrary line drawn between significant geographic points on land, and may in fact have little spatial relation to the distribtion of the spot prawn resorce. Frther stdies shold concentrate on determining optimm reserve location and

25 size. Additionally, I believe establishing reserves in other sbmarine canyon heads cold be an important part of the soltion to management of this resoce. 15

26 DEPTH AND HABITAT ASSOCIATIONS Introdction Determining patterns of spatial distribtion and relative abndance for a species is an essential contribtion to the fndamental nderstanding of marine interactions. It is especially crcial to have this type of baseline data in order to effectively model how commercial resorces are affected by hman impact over time. The spot prawn resorce makes an attractive case stdy, as it is commercially important and landings for this species are crrently on the rise in the California area. Mch of the reference material available on spot prawn distribtion and abndance is derived from fishery-dependent data. Very little is known abot the ecology of adlt spot prawns becase they occr to 4 m, depths beyond SCUBA range, therefore posing formidible logistical and financial challenges to the inqisitive ecologist. Even laboratory experiments are ncommon as the prawns' lengthy matration process (for to six years) renders them infeasible for aqacltre prposes and therefore nlikely stdy organisms (Kelly et al., 1977). Conventional methods of captt.ring target organisms in marine habitats employ gear sch as dredges, nets, traps, hook-and-line, cores, poisons, and explosives (Barry & Baxter, 1992; Parker eta!., 1994). Deep-sea research, in particlar, often tilizes trawl nets, which can introdce several biases as a reslt of potential avoidance behavior, organism escapement, nknown area trawled, and difficlty determining trawl efficiency (Bergstedt & Anderson, 199; Btler et al., 1991). Trawling is often impossible in areas sch as Carmel Canyon where the canyon walls are steep, 16

27 17 rocky, and hazardos to trawl gear. Frthermore, the whole site of conventional methods mentioned above can not be applied toward qestions comparing densities or describing habitat types in addition to what is simply present or absent (Barry & Baxter, 1992). It has only been relatively recently that towed camera sleds, remotely operated vehicles (ROVs), and hman-occpied sbmersibles have been eqipped with video cameras to enable the in sit stdy of distribtions of deep-water organisms and associated habitats (Btler et al., 1991; Robison, 1993). Videotaped transects prodce a permanent record, allowing a more extensive time for stdy of the images by mltiple researchers (Michalopolos et al., 1992; Parker eta!., 1994). Video transects also are niqe and attractive in that they are nondestrctive and repeatable (Parker et al., 1994). However, as with any new techniqe, accracy is a concern and mst be validated before proceeding with confidence. Many stdies have directly addressed problems with measring accracy margins for qantitative nderwater video transects (Btler et al., 1991; O'Connell & Carlile, 1994, Carleton & Done, 1995), sch as, Bergstedt and Anderson (199) who sed a towed camera sled and line transects to sccessflly estimate the density of a known nmber of bricks in a shallow-water lake. Accracy of deep-sea video transects can be affected by many factors, inclding sea conditions, camera resoltion, light levels, water clarity, depth, attraction/avoidance responses, topographic complexity, and the potential of reconting mobile animals (Yoklavich et al., 1993; Parker et al., 1994). Other problems inherent when sing video transects relate to navigation accracy and precision, and keeping the sbmersible a

28 18 constant distance off the bottom, with a stable altitde, pitch, and roll in order to maintain a constant field of view (Barry & Baxter, 1992; Michalopolos et al., 1992). Qestions on species abndance and habitat se have been effectively addressed in many stdies involving a wide spectrm of variations on the video transect theme (Bergstedt & Anderson, 199; Lewis, 1992; Stein eta!., 1992; O'Connell & Carlile, 1993; Yoldavich eta!., 1993; Parker et al., 1994). Nevertheless, researchers are constantly refining methods for nbiased sampling, especially the problematic isse of calclating transect areas, in an attempt to get a more accrate estimate of densities for deep-water species (Boland & Lew bel, 1986; Bergstrom et al., 1987). Traditional gear, sch as traps and trawls, are often still needed in conjnction with video transects, as it is impossible to identify or measre many organisms solely by video observations (Bergstedt & Anderson, 199; Felley and Vecchione, 1995), althogh methods are being developed to overcome the latter problem, sch as the addition of laser spots for spatial calibration (Tsting & Davis, 1992). Recent advancements developed at the Monterey Bay Aqarim Research Institte (MBARl) tilize a for-laser system, consisting of three parallel and one crossing laser, in conjnction with a cstomized software grid, to address many of these problems with image analyses (Davis & Tsting, 1991). Objectives My objectives were to se videotaped transects from Carmel sbmarine canyon to a) qantitatively and qalitatively assess habitat associations of spot prawns with regard to sbstratm composition, b) determine depth distribtion patterns of spot prawns, and c) describe species that co-occr with spot prawns.

29 19 Materials and Methods Spot prawn abndance and associated habitat were determined from 21 qantitative nderwater video transects condcted dring September 24-26, 1994 sing the two-person sbmersible, DSRV Delta (Delta Oceano graphics, Torrance, California), in Carmel sbmarine canyon (for rockfish habitat stdies by Yoklavich et al., 1995). Transects covered depths of 1-3 m on both the north and soth canyon walls (Figre 8) in a stratified systematic sampling array. Dring each transect the sbmersible pilot attempted to keep the sbmersible a relatively constant distance (approximately 2-3 m) off the canyon wall and to maintain a relatively constant speed (approximately 3 em s" 1 ) for 15 mintes of traversing. Video images were recorded on an external Hi-8 mm video camera set to maximm wide angle zoom. Two parallel laser dots fixed 2 em apart were recorded on all DSRV Delta video transects and sed to provide a frame of reference for estimating distances. All dives were condcted dring the day. Habitat patches were identified for each transect sing classes of sbstratm morphology defined in Table 3 (from Cailliet et al., npblished manscript, Moss Landing Marine Laboratories, Moss Landing, California, and Greene et al., 1995, with added phi (<I>) vales). Nmber of prawns for each distinct habitat patch was determined from the video footage, sing motion of benthic organisms to assist in identitfying the target species. Presence/absence of the conspicos and commonly co-occrring galatheid crabs, Galatlzea californiensis (Benedict, 192), Mnida lzispida (Benedict, 192), and Mnida qadri;pina (Benedict, 192), were also noted for each transect.

30 2 The area for each habitat patch was determined by captring consective frames of the 15-minte video transect and converting Hi-8 videotape to digital image files (approximately 1-2 frames per transect). This converted a strip transect into many consective qadrats. The length of each transect was measred sing the 2 em laser dots to calibrate the image analysis program, Optimas 6.2, for measring the length of each frame. Consective frame lengths in each habitat patch were then smmed to get the total length of habitat patch. The transect width was estimated at a constant 2 em for the entire transect following Yoklavich (npblished manscript, Pacific Fisheries Environmental Laboratory, Pacific Grove, California). Prawn densities (nmber m ') were then determined from the nmber of prawns conted in each habitat patch. Additional information on abndance of prawns was collected sing video from MBARI's ROV Ventana. A high resoltion, 3-chip CCD Sony DXC-3 color camera on the ROV acqired the video images which were recorded onto BetacamTM tapes. A time code embedded in the video footage is sed to correlate the video data to a depth sensor, sing a common link of Greenwich Mean Time (GMT). Post-prodction of the video footage inclded detailed annotations by MBARI scientists of organisms and geological featres observed dring a dive. A search for all occrrences of spot prawns was condcted on this large database sing the MBARI Video Information Management System (VIMS). Data were gathered from all benthic ROV Ventana dives from 1989 to 1997 when the depth recorder was fnctioning. All video images were reviewed to ensre that the annotated organisms were indeed individals of Panda/s platyceras and associated habitats were noted at this time. Depth distribtion was determined from prawn

31 conts. Three major habitat types were identified (sediment, rock, and drift algae) and 21 prawn conts per habitat type were analyzed by overall sightings and by depth. Reslts A total of 3365 frame grabs were taken from 21 video transects condcted from the DSRV Delta in Carmel Canyon. Frame lengths varied from em, depending pon the distance of the video camera to the sbstratm, with a mean of!33 em. Prawns were observed at all depths (i.e., 1-3 m). The highest prawn density per habitat patch was 2.6 m 2 on a steeply sloping sediment and gravel bottom at a depth of 2 m on the north wall of the canyon. The maximm mean density of prawns by depth was.226 m 2 for 2 m (Figre 9). Habitat types associated with prawns were not related to amont of a particlar habitat type available either overall or by depth (Figre I, Figres II a-e). Overall, sediment was the most common sbstratm type, comprising 25-3% of all bottom types srveyed (Figre I ). Highest densities of prawns occrred in habitats with complex mixtres of sediment and varios sizes of consolidated sbstrata. When analyzed by depth, mixed sbstrata consisting of massive otcrop, bolder and sediment habitat (mbs) was most abndant in the shallower depths (I and!5 m), and prawns did not occr on this habitat (Figres 11 a, 11 b). They were most freqently fond on sediment or a mixtre of sediment and massive otcrops at 1m (66% occrrence), and gravel and sediment at 15m (39% occrrence). They occrred in a more diverse array of habitats at 15m and deeper than observed at 1 m (Figres 11 a-e). Sediment habitat had the highest

32 freqency of occrrence in the canyon at depths of 2, 25, and 3 m, bt prawn 22 densities were not high in barren sediment, At these depths, prawn densities were greatest in the mixed habitats with sediment and gravel, cobbles, bolders, and massive rock otcrops (Figres lic-e), Prawns and galatheid crabs were weakly positively correlated (Table 4 ). There were only three transects where neither prawns nor galatheids were present, all at I m. Prawns and galatheids were fond together in all other transects except two shallow transects, one at!5 m and one at I m, where prawns were observed bt galatheids were not. Prawns were fond in abndance in five of the seven mid-depth transects and two of the five deeper transects. Galatheids were present in few nmbers for one of the shallow transects, , at a depth of!5 m, and in greater abndance for another of the shallow transects, , at!5 m; otherwise, galatheids were more abndant than prawns in all transects 2 m and deeper. The majority of spot prawn sightings from the ROY Ventana video were from Carmel Canyon. Adlt spot prawns were observed in depths ranging from m, with the greatest conts at m. The mean depth of adlt prawn occrrence was 195m (Figre 12). Prawns at 15m water depth were primarily associated with drift algae, and to a lesser degree with rock (Figre 14a-d). In water deeper than!5 m, fewer prawns were fond on drift algae and the majority of prawns were associated with sediment.

33 Discssion 23 From video analyses, spot prawns in Carmel Canyon were most abndant from 2-25 m. In water shallower than!5 m and deeper than 35m there were very few sightings of prawns from either the ROV Ventana or the DSRV Delta video data. Prawns were most nmeros for DSRV Delta transects in the 2m range, present bt in fewer nmbers in the deeper transects (25-3 m), and few or absent in the shallow transects (1-15 m). Balsiger (1979) reported greatest spot prawn densities from 9 to 137m, throghot the range of this species. It is possible that shallow prawn observations may have been missed by the ROV Ventana, as this ROV does not freqently dive in water depths shallower than 1 m; however, prawn sightings were also rare dring shallow DSRV Delta dives. Only two prawns were fond in waters greater than 3 m from the ROV video footage, in contrast to a reported maximm depth of occrrence of 487 m by Btler (197). The galatheid crabs were likewise infreqently observed in depths shallower than 2 m. Galatheid abndance deeper than 2 m increased notably for all transects. Prawns and galatheids were commonly fond co-occrring; however, galatheids were sally more nmeros. Prawn nmbers were not consistently large with large galatheid nmbers and visa versa. The DSRV Delta data provide clear evidence that the prawns are not simply distribted on the most commonly available habitat type. Spot prawns are habitat-specific depending on depth, bt the natre of the patterns is ndetermined. A mixed bottom composition of massive rock otcrops, bolders, and sediment made p a majority of the

34 available habitat in the shallower transects, bt prawns at those depths were fond on 24 sediment and a sediment/gravel mixtre. Conversely, while sediment habitat dominated the deeper depths (2-3 m), the prawn abndances were highest in the mixed habitats of sediment and smaller rock types sch as gravel, cobble, and bolders. Overall, this stdy fond that prawn abndance was very patchy, which is collaborated by reports fi om local trap fishers. Fishers have reported setting traps one day, procring a sbstantially large catch, then setting the rebaited line of traps in precisely the same location and coming p empty the following day. It is interesting that the prawns in the ROY Ventana video footage were most commonly fond associated with drift algae. Drift algae were not inclded as a category in the DSRY Delta transects, as these transects were concentrated on the steep canyon walls and drift algae were not reglarly seen. A majority of the ROY footage from Carmel Canyon was gathered dring transects of the axis of the canyon, where researchers have fond that piles of drift algae accmlate (Harrold et al., 1998). The decrease in prawns observed on drift algae compared to other habitat options with increasing depth is not srprising, as the amont of drift kelp available wold be expected to decrease with depth in the canyon de to decomposition and consmption by organisms sch as rchins and spot prawns. Indeed, sing some of the same ROY video footage, HmTold et al. ( 1998) fond greater densities of Macrocystis pyr(f"era components in shallow transects compared to deep transects in Carmel Canyon. As for any ecological research project, this stdy relied on many assmptions sch as the assmption that the habitat featres identified as important by the observer are also

35 25 featres recognized as important by the organism of interest (Krebs, 1989). It is difficlt to project what habitat parameters (size of the sampling nit) are appropriate. A good exercise wold be to dplicate the qantitative DSRV Delta transect analyses sing coarser categories, sch as "near rocky otcrops" or "not near rocky otcrops" for comparison to the reslts from this stdy. In addition, other biotic and abiotic factors might play larger roles than the sbstratm morphology, sch as the presence/absence of co-occrring species or even the presence/absence of other spot prawns (Pelley & Vecchione, 1995). Another assmption is that the observer sccessfi.1lly conts all target organisms within a transect (Bergstedt & Anderson, 199). While spot prawns are fairly large and generally easy to identify in the video, they potentially may be hiding in a crack or crevice or nder a bolder, which cold artificially lower the conts on rocky sbstrata. Yet another assmption is that the prawns are not positively or negatively affected by the presence of the sbmersible and indeed, the prawns dring this stdy exhibited no sign of avoidance or attractive behavior towards the sbmersible lights' that cold potentially intlence conts. Ftre video transect stdies sing the for-laser system and grid cold generate even more accrate estimates for areas and densities, and in addition, prawn sizes cold be measred in sit for different areas and different depths in the canyon. Althogh it is obviosly cost- and time-effective to tilize video data that were collected for another prpose, as Pelley and Vecchione (1995) also noted, there are inherent difficlties involved. Experimental design is limited becase there is no option for selection of location, length, time of day, time of year, and camera configration. Incorporating a

36 sampling design with a temporal aspect wold be beneficial in elcidating the patchy 26 distribtion patterns and small-scale spot prawn migrations that keep the fishers wondering and wandering.

37 GENERAL CONCLUSIONS In spite of the increase in fishing pressre to the area, Monterey prawn trap landings have remained steady at arond 5 to 15, kg per year, and 1998 cold be considered a sccessfl year for the prawn trap fishers with a record of close to 17, kg landed. Catch-per-nit-effort (CPUE) was relatively high for 1997 at.68 kg, and a little below average for 1998 at.39 kg per trap. CPUE tracked over the past 3 years shows no evidence of recent change in trends that cold possibly be attribted to the sdden rise in landings (Figre I). These factors indicate that the prawn resorce in Carmel Canyon is crrently in good condition, possibly aided by the inflence of the reserve. However, past examples from prawn trap and trawl logbook data in sothern California have shown drastic redctions in CPUE correlated with large increases in landings for I 984-I 994 (California Department offish & Game, 1995). Snada (1984) witnessed a serios drop in CPUE with a sdden increase in total catch for ridgeback prawns in the Santa Barbara Channel. Spot prawn landings for the Monterey Bay area are still on the rise with over 9, kg landed for the month of Janary I 999 alone, the majority of which is attribted to trawlers (J. Spratt, pers. comm.). Contined monitoring of this fishery will reveal how abndance is affected over time by persistently high or frther increases in landings. From fishery-independent videotape data, the highest densities of spot prawns were determined to occr in Carmel Canyon from I 5-3 m in depth. Prawns are habitat-specific by depth, not fond associated with the most common habitat types available. The highest prawn density per habitat patch was 2.6 rn- 2 on a steeply sloping 27

38 sediment and gravel bottom at a depth of 2 m on the north wall of the canyon. The 28 highest mean prawn density by depth was.226 m- 2 for 2 m. Spot prawns were fond to be commonly associated with galatheid crabs and piles of drift algae fond in the canyon axis. Ftre video transect stdies shold make se of a mlti-laser system to improve accracy in estimating area srveyed and organism sizes, and shold inclde a temporal factor, which cold prove to be of great importance in nderstanding distribtion patterns of spot prawns.

39 3 LITERATURE CITED Balsiger, J.W A Review ofpandalid Shrimp Fisheries in the Northern Hemisphere: Proceedings of the International Pandalid Shrimp Symposim. Sea Grant Report pp. Barr, L Stdies of spot shrimp, Panda/s platyceras, at Little Port Walter, Alaska. Mar. Fish. Rev. 35: Barry, J.P., and C.H. Baxter Srvey design considerations for deep-sea benthic commnities sing ROVs. Mar. Techno!. Soc. J. 26(4):2-26. Bergstedt, R.A., and D.R. Anderson Evalation of line transect sampling based on remotely sensed data from nderwater video. Trans. Amer. Fish. Soc. 119: Bergstrom, B.I., Larsson, J., and J.O. Petersson Use of a remotely operated vehicle (ROV) to stdy marine phenomena: I. Pandalid shrimp densities. Mar. Ecol. Pro g. Ser. 37: Bohnsack, J.A The potential of marine fishery reserves for reef fish management in the U.S. Sothern Atlantic. Plan Development Team. Reef Fish Management Plan. NOAA Technical Memorandm. NMFS-SEFC-261, 4pp. Bohnsack, J.A Marine Reserves: They enhance fisheries, redce conflicts, and protect resorces. Oceans Fall 1993: Boland, G.S., and G.S. Lew bel The estimation of demersal fish densities in biological srveys sing nderwater television systems. Oceans 1986 Conference Record: Systems, Strctres and Analysis. 1:9-13. Btler, J.L., Wakefield, W.W., Adams, P.B., Robison, B.H., and C.H. Baxter Application of line transect methods to srveying demersal commnities with ROVs and manned sbmersibles. Proceedings, Oceans 1991 Conference 2: Btler, T.H Growth, reprodction and distribtion ofpandalid shrimp in British Colmbia. J. Fish. Res. Bd. Canada 21 (6): Btler, T.H Synopsis of biological data on the prawn Panda/s platyceras Brandt, FAO Fish. Synopsis 95: