FIELD ASPECTS OF THE SEPIOLID SQUID ROSSIA PACIFICA BERRY, 1911

Transcription

1 FIELD ASPECTS OF THE SEPIOLID SQUID ROSSIA PACIFICA BERRY, 1911 Roland C. Anderson The Seattle Aquarium Pier 59, Seattle, WA U.S.A. A SCUBA survey of Rossia pacifica conducted in Puget Sound (Washington State) found the squid at a number of sites in areas of low current, muddy sand, and moderately sloping bottoms. More squid were found than expected. Seasonal migrations related to temperature were monitored. (Paper first presented at 1987 annual meeting of Western Society of Malacologists) INTRODUCTION Rossia pacifica Berry, 1911, is a North Pacific sepiolid squid first described by Stillman Berry (1911, 1912). Although it is not a teuthid, it is commonly called a squid, and in particular, the stubby squid, short squid or bob-tail squid. It is common ':hroughout the boreal North Pacif:c: ranging from Japan, the Aleutian Islands, Alaska to Southern California (Akimushkin, 1965; Roper et ai, 1984). It spends daylight hours buried in the sand or mud and emerges at night to swim and/or lie in wait of prey, primarily small shrimp (Summers, 1985; Anderson, in press). General accounts of the animal can be found in various popular works such as Hochberg and Fields (1980), Barr and Barr (1983), Flora and Fairbanks (1977), and

2 Coldwater Diving For Science Hewlett and Hewlett (1976). For the most part, biological aspects and observations of the animal have been determined by trawl capture and in the laboratory (Brocco, 1970; Summers, 1985). Brocco studied distribution, habitat, habits, food, reproductive biology, and population studies. Summers has reared the squid through several generations in the laboratory and added to Brocco's life history data. Neither made in situ observations, nor observations of the animal in Puget Sound, Washington. Shimek reported on escape behaviors as observed by SCUBA at Friday Harbor, Washington, and Anderson (in press) reported on diver collection of the squid and its behavior and exhibition at the Seattle Aquarium (S.A.). As previously reported in Anderson (in press), S.A. divers had found the squid infrequently in water m deep in the sandy or muddy areas of central Puget Sound. S.A. divers had not reported seeing R. pacifica in the summer and only rarely during the daytime in the winter. Based on this experience, determination was made to conduct a survey throughout one winter and spring in an attempt to locate areas in Puget Sound where R. pacifica might be found reliably by divers in order to supply the S.A. exhibits and research. In addition, water and substrate conditions, population densities, and seasonal migrations would be monitored. METHODS Weekly night SCUBA dives were conducted during the fall, winter and spring of from shore access areas within two hours' travel time from Seattle, at sites where R. pacifica were likely to be found. These sites were selected for moderately sloping bottoms, sand-silt substrate conditions, lack of strong currents, previous sightings, and night-time accessibility. Dives were made approximately two hours after sunset and were performed by divers who had previously seen R. pacifica and could recognize them. Dives were confined to sport diving depths «30 m) and also conformed to City of Seattle diving regulations. Dive durations were close to 40 minutes and they extended over approximately 100 m of bottom distance. When R. pacifica were spotted, the depth and water temperature were noted. Some water samples were taken for ph and salinity determinations, and bottom samples were taken in some areas of high squid sightings for sediment analysis. Salinity and ph were measured at the S.A. laboratory and sediment analysis was 2

3 ANDERSON. Field aspects of Rossia pacifica performed by the University of Washington Oceanographic Laboratory. A sediment sample at one non- R. pacifica site was taken for comparison; it appeared to be clean sand. Slope was measured in areas of high R. pacifica sightings with an elementary inclinometer. Tidal currents were recorded based on diver observations. Some R. pacifica were captured for display and holding at S.A. but most were left undisturbed. One site with a high number of sightings (7/dive), was selected for more intensive survey and no squid were taken from that site (Dash Point, Tacoma, Wa.). Three monthly "mass" dives were conducted at this location to determine population density and distribution during the spring of 1987 over a pre-set distance of 100 m. RESULTS A total of 69 R. pacifica were observed from 28 September 1986 to 23 May 1987 during 23 dives specifically looking for the 3

4 Coldwater Diving For Science squid. These were found at 11 sites between Seattle and Tacoma, one site on Hood Canal and one site on Burrows Bay. The central Puget Sound sites are depicted in figure 1. The average slope of the bottom where they were found was 140. Salinity and ph did not vary appreciably between sightings and did not differ from readings taken at S.A.; average values were 28.5 ppm and 7.8 respectively. Results of the sediment analysis are given in figure 2. Bottom Samples Average of 3 Rossia sites 1 non-rossia site Sand Silt Of. %N Sand Silt Of. %N Figure % 13.35% 0.575% 0.169% 96.75% 3.25% 0.172% 0.012% Average depths of R. pacifica sightings by month are shown In figure 3 along with average monthly temperatures (as recorded at S.A., at 15 m depth). o 1~ 70' II 1, 60' 10-50' WI 40' X 0 X 0 II X 0 0! ~ II II 0 fit 30' SEPT OCT NOV DEC JAN FEB MAR APR MAY n= N = 69 FIGURE 3 4

5 ANDERSON. Field aspects of Rossia pacifica At Dash Point, the site selected for a mass survey, 25 R. pacifica were found within a shoreline distance of 100 m by six divers in April; two were found May, and none in June. DISCUSSION Rossia pacifica had been considered a rare find by S.A. divers, but on the basis of this survey, it can be seen that it is found at more sites, in greater numbers, and at shallower depths than previously understood. As demonstrated here, fewer squid were seen in early summer months based on our mass survey dives at Dash Point. Summers (1985) found that adult squid mated, spawned and died in the late spring and early summer. This is corroborated by my experience in keeping the squid at S.A. where they spawn and die in May and June. Brocco's (1970) population on the east side of Vancouver Island, Canada, spawned and died in August and September when the warming water temperature approached 110C. He suggested that the higher temperature acted as a stimulant to spawning. Correspondingly, the R. pacifica at S.A. spawn in May when the sea water temperature reaches 110C (see figure 3).. Spawning and death effectively eliminates half the population since they have a two-year life span. This leaves juveniles with about 10 mm dorsal mantle length and eggs (Summers, 1985). The small individuals are certainly more difficult for divers to spot. Summers (1985) trawled R. pacifica in the summer.in depths of m and Brocco (1970) trawled them in fathoms, all in depths beyond our diving range. Ronald L. Shimek, biologist and diver/photographer has seen R. pacifica while diving in Friday Harbor Bay (Washington) in the summer, but in decreased numbers (pers. comm.) He attributes the decrease in numbers only to the post-spawning die-off. This population is different from the one we worked with, and Friday Harbor Bay has lower temperatures than Puget Sound. In this study, R. pacifica were typically found on moderately sloping bottoms (average 140), the slope of which continued down to the cold depths of Puget ~ound (>300 m), so it would not be difficult for them to move deeper. R. pacifica have been caught in shrimp trawls deeper than 80 m in Puget Sound (Daniel Doty, U. Washington, pers. comm.). There is evidence that other cephalopods in the area make depth migrations, such as Octopus dofleini Wulker, 1910, for example (Mottet, 1975). Clues for such migrations may be 5

6 Coldwater Diving For Science temperature, amount of daylight, food supply, or reproductive stimuli. In this case I believe it to be temperature, as demonstrated by figure 3. It can be seen from the sediment analysis that R. pacifica were found in muddy sand containing fine sediments and organics. We did not find any on pure mud or clean sand, but rather in areas somewhat protected from Puget Sound's. strong tidal currents, hence the muddy sand. Some R. pacifica were found in Tacoma and Seattle harbors and outside Seattle's largest pleasure boat marina, areas which contain polluted bottom sediments (Puget Sound Water Quality Authority, 1987). It is not known what effect being buried much of the time in these sediments has on R. pacifica. Possibly, the considerable mucus it is able to secrete serves as a protectant. I believe estimates of the number of R. pacifica in Puget Sound have to be adjusted upwards. The squid was found at nearly all dive sites selected between Seattle and Tacoma, a shoreline distance of about 48 km. Twenty five R. pacifica were found within 100 m in diving depths in one limited survey, and this site was probably not unique. While extrapolation of the numbers from that limited area to the whole shoreline distance would be unwise, it can be concluded that R. pacifica are far m ore common than previously thought. ACKNOWLEDGMENTS The following divers braved the elements and dove at night to help me look for squid this last winter: Bill Robertson, Dan and Doyla Doty, Joy Vanderwerff, Bill Bruin, Bill Engelhardt, Pat McMahon, Richard Hocking, Rick Slightam, Walt Rostykus, and Jeff Christiansen. Thanks also to the Tacoma Metropolitan Park Department for letting us dive at Dash Point Park after hours, to the Seattle Aquarium graphics department for preparing figures for this paper, to Katherine Krogslund at the University of Washington Seawater Chemistry Lab for performing sediment analysis, and especially to Dr. William C. Summers at Western Washington University for encouragement and reviewing this manuscript. LITERATURE CITED Akimushkin, Cephalopods of the U.S.S.R. Translation of the 1963 Russian edition by A. Mercado. Jerusalem. 223 pp. 6

7 ANDERSON. Field aspects of Rossia pacifica Anderson, R. C. in press. Cephalopods at the Seattle Aquarium. Zoo Yearbook London. Int'l. Barr, L. and N. Barr Under Alaska Seas. Alaskan N.W. Pub!. Co. Anchorage. 208 pp. Berry, S. S Preliminary notes on some new Pacific cephalopods. Proc. U. S. Nat. Mus. 40: Berry, S. S A review of the cephalopods of Western North America. Bull. U. S. Bur. Fish. 30: Brocco, S. L Aspects of the biology of the sepiolid squid Rossia pacifica Berry. M. S. Thesis Univ. of Victoria, B.C. Canada. 151 pp. Flora, C.J. and E. Fairbanks The Sound and the sea. 3rd edition. Wash. Dept. of Printing, Olympia, Wash. 474 pp. Hewlett, S. and K. G. Hewlett Sea life of the Pacific Northwest. McGraw Hill 176 pp. Hochberg, F. G. Jr. and W. G. Fields Cephalopoda: the squids and octopuses. In: Intertidal invertebrates of California. Ed.: R. H. Morris, D. P. Abbott and E. C. Haderlie Stanford Press. 690 pp. Mottet, M. G The fishery biology of Octopus dofleini (Wulker). Tech. Rep. 16. Wash. State Dept. Fish. 37 pp. Puget Sound Water Quality Authority, Puget Sound Water Quality Management Plan, Katherine Fletcher, chair. P. S. W. Q. A. Seattle, Wash. 212 pp. Roper, C. F. E., M. J. Sweeney, and C. E. Nauen FAO species catalog. Vol. 3. Cephalopods of the world. FAO Fish. Symp. (123) 3: 277 pp. Srumek, R Escape behavior of Rossia pacifica Berry, 1911 (abstract). Am. Malacol. Bull. 2: 91 Summers, W. C Ecological implications of life stage timing determined from the cultivation of Rossia pacifica (Mollusca: Cephalopoda). Vie Milieu 35:

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