New Zealand Journal of Marine and Freshwater Research

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1 New Zealand Journal of Marine and Freshwater Research ISSN: (Print) (Online) Journal homepage: Using acoustic tagging to determine adult spiny lobster (Panulirus argus) movement patterns in the Western Sambo Ecological Reserve (Florida, United States) Rodney D. Bertelsen & Jessica Hornbeck To cite this article: Rodney D. Bertelsen & Jessica Hornbeck (2009) Using acoustic tagging to determine adult spiny lobster (Panulirusargus) movement patterns in the Western Sambo Ecological Reserve (Florida, United States), New Zealand Journal of Marine and Freshwater Research, 43:1, 35-46, DOI: / To link to this article: Published online: 19 Feb Submit your article to this journal Article views: 655 Citing articles: 22 View citing articles Full Terms & Conditions of access and use can be found at

2 New Zealand Journal of Marine and Freshwater Research, 2009, Vol. 43: /09/ The Royal Society of New Zealand Using acoustic tagging to determine adult spiny lobster (Panulirus argus) movement patterns in the Western Sambo Ecological Reserve (Florida, United States) RODNEY D. BERTELSEN JESSICA HORNBECK Florida Fish & Wildlife Conservation Commission Florida Wildlife Research Institute 2796 Overseas Highway, Suite 119 Marathon, FL United States Abstract We used acoustic telemetry to study the movements of spiny lobster (Panulirus argus) during the spring and summer of 2003 and 2004 in Hawk Channel in the Western Sambo Ecological Reserve near Key West, Florida, United States. Overall, lobsters generally showed greatest movement after sunset and before sunrise with relatively less movement between midnight and 0200 h, however, there was great variability in movement patterns between individual lobsters and these variations were related to size or sex. Little or no movement occurred during daytime. Patterns of movement, as revealed by acoustic telemetry revealed that some lobsters repeatedly travelled to the same foraging area at the same time and then returned to the same patch reef (homing ability). Female lobsters that were reproductively active, exhibited movement patterns consistent with reproductive migrations to the forereef. These migrations lasted approximately 1 week and the lobster returned to the same patch reef presumably using the same homing ability used during daily activities. Although not statistically significant, the greatest overall daily total movement (total distance travelled) was found in small females. Small females also showed the greatest net daily movement (distance between denning locations) which suggests they had the highest rate of changing dens. The greater daily movement of small females did not convert to greater home ranges. There was no pattern in home range size with respect to the size and sex of lobsters. M07083; Online publication date 24 February 2009 Received 30 November 2007; accepted 16 November 2008 Keywords acoustic telemetry; movement; reproductive migration; marine reserve; homing; home range INTRODUCTION Research focusing on the movement of lobsters including Panulirus argus (Latreille, 1804) has been reviewed and summarised by Herrnkind (1980) and Childress & Jury (2006). In these reviews, lobster movements were primarily categorised spatially as: (1) homing; (2) nomadic; or (3) migratory (Herrnkind 1980) and temporally as: (1) daily; (2) ontogenetic; or (3) seasonal (Childress & Jury 2006). Factors known to guide the movements of P. argus include the earth's magnetic field (Lohmann 1984; Lohmann et al. 1995; Boles & Lohmann 2003), hydrodynamic forces such as wave surge (Herrnkind & McLean 1971; Nevitt et al. 1995), visual (Schöne 1961), and chemical cues (Nevitt et al. 2000; Horner et al. 2004). Visual cues probably play only a minor role in guiding lobsters, as much of their movement occurs at low light levels (Herrnkind 1980). In general, bright full moonlight can suppress movement in clear shallow waters (Sutcliffe 1956). Studies designed directly to determine movement patterns of adult lobsters have used techniques such as tag-recapture (e.g., Gardner et al. 2002; Kelly & MacDiarmid 2003; Linnane et al. 2005), visual tracking, acoustic telemetry (e.g., Kelly 2001; Hovel & Lowe 2007), or a combination of all these techniques (Herrnkind et al. 1975). Although each technique has strengths and weaknesses (see Herrnkind 1980), both reviews (Herrnkind 1980; Childress & Jury 2006) noted the potential of acoustic telemetry. The Tektite-II programme in the United States Virgin Islands (Cooper & Herrnkind 1971; Olsen et al. 1972) conducted during 1970 and 1971 was the first to incorporate extensive use of acoustic technology with diver observations in a lobster movement study. In the Tektite-II programme, small transmitters were fixed to lobsters, then tracked with directional hydrophones which provided the identity

3 36 New Zealand Journal of Marine and Freshwater Research, 2009, Vol. 43 and direction to a given lobster. although each lobster needed to be tracked individually, acoustic telemetry provided the means to track a lobster with a minimum of obtrusion and lobsters could be tracked in total darkness. These efforts permitted the detailed description of temporal patterns of lobsters shifting their daytime shelters, the frequency of these changes, paths to foraging grounds, and peak activity times (olsen et al. 1972). Since then, acoustic technology has advanced to where coded tags can now be tracked passively and unattended using a grid of omni-directional data logging hydrophones (e.g., Simpfendorfer et al. 2002; Giacalone et al. 2005). one exploited animal that has been monitored and managed extensively in south Florida, United States, is the caribbean spiny lobster (P. argus). Herein we focus on movement patterns of adult P. argus determined by acoustic telemetry. MATERIALS AND METHODS Study site The study was conducted within the Western Sambo ecological Reserve (WSeR). WSeR was established in July 1977 within the Florida keys National Marine Sanctuary (FkNMS) by the National oceanic and atmospheric administration (Noaa). its purpose is to protect marine life and provide replenishment of marine life into the surrounding areas (department of commerce 1996). located near key West, Florida, WSeR covers 3000 ha extending from the shoreline of Boca chica key to the Western Sambo reef (Fig. 1a). The reserve is 4 km wide at Boca chica and nearly 3 km wide at the reef track. The distance from shoreline to reef tract is approximately 8 km. extending through the middle of the reserve from east to west is a region known as Hawk channel. The bottom of the channel forms a generally flat substrate comprising mud, sand, or seagrass. The flat channel is punctuated by patch reefs and octocoral halos around the patch reefs. The depth of the channel ranges between 9 and 11m whereas the patch reefs rise to within 6-4 m of the surface. a typical patch reef in this part of Hawk channel is approximately m in diameter (FWc unpubl. data). The extent and location of each habitat type are largely unknown because of poor water clarity. during our studies, visibility was generally less than 4 m at the surface and less than 1-3 m at the bottom. Acoustic tagging We tagged a total of 10 lobsters in May 2003 (pilot study), five males (mean ± SD: 95.8 ± 17.0 mm carapace length, CL) and five females (80.6 ± 14.3 mm CL). Two of the five females were reproductively active (egg-bearing, ripe ovary, or spermatophore present) at the time of tagging. We tagged a total of 39 lobsters in late May and early June 2004,21 males (97.3 ±18.6 mm CL) and 18 females (82.3 ± 12.6 mm cl). Because male lobsters are considerably larger than females in WSeR (cox & Hunt 2005), we tagged markedly more large males (no females were found in the >110 mm cl size class). Seventeen of the females were reproductively active at the time of tagging. lobsters were captured by ScUBa divers who brought the lobsters to a boat for tagging. lobsters were kept in a shallow tray filled with sea water, allowing them to maintain water flow over their gills during tagging. Tags were glued onto the lobsters' carapace by using a fast-setting plumber's epoxy cement (AquaMend Polymeric Systems, inc., Pennsylvania, United States). Within 20 minutes, divers returned each lobster to their den. observations of tagged lobsters kept in large (3 m diam.) holding tanks confirmed that tags remain on the lobsters until moulting (R.d. Bertelsen pers. obs.). one tag placed on a female was detected only once on the first day and was presumed either lost or failed. The tags (VeMco, V16 coded tags) were 16 mm in diameter, 58 mm long and produced a coded signal in a randomised interval between 60 and 180 s. The randomised interval prevents the possibility of code collision events between any two given tags over time (lacroix & Voegeli 2000). Tags transmit at 69 khz frequency with a power rating of 158 db re µpa at one meter. one year before deployment of receivers, we conducted range tests of our tags at Washerwoman shoals (a Hawk channel patch reef area similar to WSeR) (FWc unpubl. data). The range tests consisted of stationing receivers between 50 m to 1 km from tags placed in open areas of Hawk channel and in the patch reefs. Tests were repeated 3 times in open areas and 3 times in the patch reefs. We found that tags placed outside patch reefs could be reliably detected (>50% detections/transmissions) at a distance of m. When tags were placed in patch reefs, detection became highly unpredictable but was generally less than 100 m. during June of 2003 and 2004, 20 and 22 (respectively) omnidirectional VR2 (VeMco) acoustic receivers were placed into grids along the

4 Bertelsen & Hornbeck Spiny lobster movement patterns ^ W 81.7 W Receiver locations deploymert X 2008 deployment 1 WSB3 boundary Bottom contours Fig. 1 A, location of the Western Sambo ecological Reserve in south Florida, United States. dashed lines indicate contour depth lines. B, Deployment map of the receivers for 2003 and Receivers were placed along the eastern boundary of the Western Sambo ecological Reserve near mid-hawk channel. in 2004, an additional four receivers were placed near the reef tract.

5 38 New Zealand Journal of Marine and Freshwater Research, 2009, Vol. 43 eastern boundary of WSeR in Hawk channel (Fig. 1B). The inter-receiver distance was 200 m in 2003 and 450 m in in 2004, we also placed four receivers behind the forereef of WSeR (Fig. 1B). all receivers were placed onto soft bottom sand or mud using a concrete pad and a 1.5 m PVc pole. in 2003, the grid was placed along an east-west and north-south line. in 2004, we placed the grid in an elliptical pattern with the main axis running northeast to southwest. The forereef receivers were placed to the southwest of the elliptical grid. The reason for this pattern was a southwest migration direction detected in female lobsters during the 2003 pilot study. The receivers were left in place for 42 days in 2003 and 52 days in during 2003, one receiver in the grid flooded, however, we recovered its data from the first half of the study. The receiver configuration allowed us to track lobsters with precision to approximately 30 m. The precision of our location estimates was determined by the hourly centroids of a tagged lobster that had entered a trap, which fell within a 30 m radius. The 2003 data were used to characterise movement tracks on a daily and hourly basis as well as documenting den shifting, foraging, and the possibility of migration potentially associated with spawning. The size of this grid was too small to determine home ranges because lobsters often walked out and back onto the grid, therefore the grid was expanded in 2004 to approximately 3 km 2 km. This larger grid increased the inter-receiver distance to an average of 450 m which reduced the effectiveness of the grid's tracking capabilities, but permitted larger scale measurements including estimation of home range sizes and daily total distances travelled (Fig. 1B). Usable telemetry data were acquired from all 10 tags during 2003 when tags were detected from 7 to 42 days. during 2004, one of the 39 tags placed on a reproductively active female lobster, was detected only once. The other 38 tags were detected from between 2 and 52 days. Data processing The acoustic receivers recorded a tag number, date and time to the nearest s. These data were maintained by each receiver in a non-volatile memory chip. The data from each receiver was downloaded as a text file to a PC using a magnetic probe provided by VeMco. To these data we added the latitude and longitude of each receiver. Because clock speeds vary slightly between receivers, we adjusted the time of each record in the database by any given receiver to a "standard" time based on the slowest receiver clock (corrections are generally on the order of a few s and exceptionally a few min). The adjustment was made by determining a linear regression relationship between each receiver's clock speed. The difference in the clocks was measured by placing all receivers in a common pool of water and "time stamping" them at the beginning and end of the project with a coded tag held in reserve. Next, centroids for a 1 h time period were calculated as a simple weighted mean of latitude and longitude for each tag and stored on another database. overall, in a 1 h time period, a given tag would be recorded on average 44 times on 4.5 receivers in 2003 and 16 times on 3.5 receivers in For generating tracking data, a running 1 h centroid was calculated for all possible 15 min of elapsed time. Hence, a centroid for the 0100 h to 0200 h period was calculated, then 0115 h to 0215 h, and so on. To estimate distance travelled or location for a given time of day, separate 1 h centroid estimates (without the 15 min running mean) were calculated, then the distance and velocity were estimated using the haversine formula (Sinnott 1984). estimating den locations (daytime positions) was the most difficult calculation in this study. Rough bottom topography can both obscure and reflect acoustic signals (Pincock & Voegeli 1990). Whereas Herrnkind (1975) reported approximately a one order of magnitude loss in detection distances of tags when lobsters enter rough hard bottom, we experienced a loss of more than two orders of magnitude in detection distance while testing tags in Hawk channel using receivers at fixed locations (FWC unpubl. data). Den locations were thus estimated using three methods depending on the amount of data available. The first method was to combine all tag receptions for one daylight period into one centroid. This method can provide reliable results if the tag is detected by more than 4 receivers (indicating the lobster is not deep inside rocky structures), but in many instances only one receiver detected the tag or none. The second method was to use the tracking data before sunset and just after the next sunset to extrapolate a position. This method also becomes unreliable as lobsters approach rough hard bottom areas. a third method was to estimate a daily evening position by calculating a centroid for 2000 h. although this time represents a period when lobsters are about to move at a rapid pace, it is also the time closest to daylight for which we had the greatest amount of data. local time for sunset in June was between 5 and 20 min after 2000 h.

6 Bertelsen & Hornbeck Spiny lobster movement patterns 39 Tracking data and den location estimates were analysed using Spatial analyst, Tracking analyst (esri) and animal Movement extension (Hooge & eichenlaub 2000). We used these tools to chart daily movement patterns, measure the size of home ranges, determine migration paths, and nomadic departures. differences in total daily movement among size classes of lobsters were explored using one-way ano Va (Sokal & Rohlf 1995). The association between the size of lobster and size of home range was determined with Pearson's correlation coefficient (Sokal & Rohlf 1995). RESULTS Daily movements overall, the mean for average daily total movement for WSeR patch reef dwelling lobsters was nearly 900 m per day with females moving on average slightly more than males, 923 versus 871 m/day, respectively (Table 1). By sex and size class, the greatest average total daily movement was nearly 1300 m per day by <75 mm cl females (Table 1), however, the total daily movement by these small females was not statistically different from any other size class (anova; d.f. = 3; F = 1.57; P > 0.24). The males' total daily movements were consistent among size classes and likewise not statistically significant (ANOVA; d.f. = 2; F = 0.82; P > 0.50). The relatively low number of days (95) of daily total movement estimates for mm c l sized females was because by chance, four of the seven females migrated to the forereef (thus outside of the grid) in less than a week after tagging. WSeR patch reef dwelling lobsters showed the greatest movement after sunset and before sunrise. For 2-3 h after sunset we estimated the mean velocity of lobsters at greater than 100 m/h with a similar but slightly lower peak before sunrise (Fig. 2). during nighttime hours, mean velocity slowed to approximately 75 m/h around 0200 h. little movement occurred during daytime. daytime movements appeared to average around 30 m/h, but most of this estimated velocity was owing to random variation in the reception of each ping from the tags and not to actual movement. in addition, the 2003 data revealed one female lobster returning to the grid after a forereef migration. it arrived an hour after sunrise to a patch reef 400 m to the east of its "home" patch reef. late in the afternoon, the acoustic data suggested that it left the temporary patch reef before sunset, then returned until sunset, before it travelled back to its "home" patch reef and resumed its typical movement patterns that night. as stated previously, a lobster at rest appears to move at approximately 30 m/h owing to the level of precision provided by the grid. as with Table 1 overall daily movement statistics of male and female lobsters by size class plus number of potential reproductive migrations by female lobsters and emigrations by male lobsters. daylight "movement" was removed, because the method used to calculate positions randomly varied by approximately 30 m, and daylight movement was primarily owing to this precision error rather than to real movement. Size class (mm) Females < Totals Males < >110 Totals n u lobster days average daily total movement (m/day) Mean±SEM 1266± ± ± ± ± ± ±76 Potential reproductive migrations No. of No. of spawners spawning trips emigration status after 54 days on grid gone unknown eighteen female lobsters were tagged, but 1 tag was detected only once and was therefore excluded from analysis.

7 40 New Zealand Journal of Marine and Freshwater Research, 2009, Vol Hour Fig. 2 Mean (±95% confidence limits of the means, n = ) hourly movement rates (m per h) of lobsters within Hawk channel, Western Sambo ecological Reserve, United States during June-July 2003 and the overestimated daytime velocities, the nighttime minimum of 75 m/h was overestimated to the extent that lobsters move slowly or not at all while foraging. We found considerable variation in the hourly velocity profiles among individual lobsters with no patterns related either to size or sex. For example, the largest male's (117 mm CL) estimated hourly velocity did not exceed 50 m/h and it was among the slowest lobsters. The next largest male's (116 mm cl) estimated hourly velocity exceeded 200 m/h at 2200 h and 0400 h and it was among the fastest lobsters. Similarly, the two largest tagged female lobsters' (105 mm CL) estimated hourly velocities showed similarly divergent profiles. We estimated the daily shifts in the location of each lobster by examining the distance between sequential daily evening positions. overall, approximately 30% of the daily location shifts in lobsters were more than 100 m. Female lobsters showed a trend toward decreasing net daily shifts in location with increasing size (Fig. 3). Small female lobsters (<75 mm cl) changed their daily location more than any other size class for either sex. They changed location by more than 100 m more than 50% of the time. Small males (75-89 mm cl) did show slightly greater shifts in daily location than very large males (>110 mm cl), but the shifts of small males were slightly less than those of same sized females (Fig. 3). one 77 mm c l non-reproductive female lobster tagged during 2003 remained within the grid through most of the 42-day deployment of receivers thus permitting detailed examination of daily tracks. For much of this time, this lobster had a routine of emerging from several den locations in the northeast quadrant of the grid after sunset, then travelling south for about m (Fig. 4a). From approximately midnight to 0200 h, movement typically slowed and meandered. By 0300 h, movement increased and was directed northward toward various den locations. These dens were located within 100 to 200 m of each other. Twice during the 42 days, this lobster moved to more distant den locations. one distant den was more than 600 m away in the southwest corner of the grid (Fig. 4B). Two periods of slower movement occurred during this trip. The first slowdown occurred near 2200 h when it was near the area where it typically slowed down on previous nights between midnight and 0200 h, and the second slowdown location was a new location in the west central part of the grid at 0100 h. it returned to its primary shelter area the following night, taking a different return route moving 500 m to the north outside the grid's western boundary, then turning east travelling another 600 m (Fig. 4B). The second distance den was located outside the grid's northern boundary. as with the previous example, the lobster returned to its primary shelter area the following night. Potential spawning migrations during the 2003 project, we discovered a distinct movement pattern in three of the five tagged female lobsters, which began a sudden southerly straightline movement around midnight, culminating with each female exiting the southern boundary of the grid at a velocity of between 250 and 500 m/h. one of these lobsters returned to the same patch reef within the grid 1 week later, then 3 weeks later, and a second departure and return occurred three weeks after the first return. In both instances, showing precise navigational skills, this lobster returned to the same patch reef (Fig. 4c). None of the male lobsters exhibited similar movement behaviour, although we tracked one male following the path of a female on a forereef migration, but this male travelled only 300 m before turning and its movement occurred approximately 30 min and 150 m behind the female. considering this rapid female movement toward the reef track to be a spawning migration, we placed four receivers on approaches to the forereef during We did not have sufficient receivers to completely cover

8 Bertelsen & Hornbeck Spiny lobster movement patterns 41 Fig. 3 Frequency of daily net shifts in location of lobsters by sex and size class. A, females; B, males. daily net shift in location corresponds to the difference in metres of the estimated location of a lobster through a 24-h cycle. The location of each lobster was determined by acoustic data during the h period which corresponds to sunset and twilight (approximately when lobsters emerged from shelters). No female lobster greater than 105 mm carapace length (cl) was tagged; only single males (data not shown) at <75 mm and mm cl were tagged. n= 5 SÍ28 class (mm CL) Size class {mm CL] July 2003 B July 2003 i C 9 July 2003 ' 1900 ' ' ?" li '0030 I t t July July ' ut l I' O 2000 Fig. 4 Representative nightly tracks of lobsters from the 2003 tracking data showing : A, repetitive daily movements ; B, den shifting; and c, potential reproductive migration. Tracks for a and B were from a non-reproductive 77 mm carapace length (cl) female and for c from an egg-bearing 105 mm cl female. Two examples (in columns) are given for each category of movement. in c, the lobster left the grid then returned a week later. 200 m all approaches to the forereef, thus some southerly departures from the grid were not detected. of the 17 female lobsters tagged (15 carried eggs at the time of tagging), 11 females made spawning trips and three of these made a second trip (Table 1). Four of these 11 females were not detected by the forereef receivers and presumably spawned elsewhere. Two egg-bearing lobsters' movement records were inconclusive and incomplete. Finally, 2 other egg-bearing lobsters did not leave the grid and presumably spawned in Hawk channel. There were no differences in the proportion of females making forereef migrations by size class and one female in each size class made a second trip (Table 1).

9 42 New Zealand Journal of Marine and Freshwater Research, 2009, Vol Size (mm CL) Fig. 5 Homerange (m 2 ) (minimum convex polygon) by lobster size (mm carapace length, cl). excluded are lobsters that emigrated or made reproductive migrations hence the relative rarity of female lobsters. (open circles, males; closed circles, females.) As with hourly movement profiles, lobsters in Hawk channel showed considerable variability in estimated home ranges. Home range estimates ranged approximately one order of magnitude from less than m 2 to nearly m 2. The size of the lobster showed no relationship with the size of home range (Pearson's correlation; r = , P> 0.354) (Fig. 5) We attempted to determine a most likely fate of each tagged lobster, noting for example if the last signals were detected in the middle or edge of the grid and if detection ended on the edge of the grid, we noted the direction. of the 21 male lobsters tagged, 12 males were present when the receivers were recovered or were detected within the grid 80% of the time. Four males moved to edge receivers then left the grid (25% of male lobsters with known fates). The remainder of the males had ambiguous fates. We did not attempt to characterise female lobsters in this manner because their departures from the grid were directed toward the forereef and in many cases we detected a return after approximately 1 week. discussion overall, we found acoustic technology to be an invaluable tool to evaluate the movements of the spiny lobster population in WSeR. There was little or no chance that the forereef migrations of reproductively active female lobsters could have been detected without acoustic tags and receivers, because the area rarely has water clarity that permits long-term direct diver observations such as those during the Tektite-ii project (olsen et al. 1972). The grid of receivers worked well primarily because the area surrounding the patch reefs (which sheltered the lobsters during the daytime) was flat and open. Panulirus argus adults stay in shelters during the daytime and rarely move unless provoked (Herrnkind et al. 1975). The only exceptions to this observation is that we occasionally observed males moving in daylight during the breeding season (R.d. Bertelsen pers. obs.). Some disadvantages to tracking spiny lobsters using acoustic tags and a grid of receivers versus direct diver observations are: (1) there are distortions in the estimated location of lobsters that are located near the edge of the grid or outside the grid; (2) the range of tag detection and consequently the reliability of estimated locations is greatly reduced when lobsters approach and enter rough rocky habitat (see Giacalone et al. 2005); and (3) without direct observations of lobsters, behaviours such as foraging can only be inferred. in addition, tags are lost at the time of moulting, therefore, limiting the time a single lobster can be tracked. equipment failure or loss (e.g., owing to boats snagging and dragging off a receiver stand) is also a disadvantage if servicing trips are infrequent. Daily movements Panulirus argus was once considered a "sluggish" animal but perhaps capable of long-distance movements and likely incapable of returning to the same den "except by accident" (crawford & de Smidt 1922). Since then, many investigations have found adult P. argus to be capable of long distance movements (e.g., Gregory & labisky 1986; Hunt et al. 1988) and P. argus does have geo-spatial knowledge of many dens in its local home area (Herrnkind et al. 1975; Herrnkind & Redig 1975). Potential cues that guide P. argus' movements include light (Schöne 1961), wave surge (Herrnkind & Mclean 1971; Nevitt et al. 1995), and odours (Horner et al. 2004), but for Hawk channel spiny lobster, the GPS-like geomagnetic compass ability (Boles & lohmann 2003) seems to be the only consistent cue available to guide their movements. Water clarity in Hawk

10 Bertelsen & Hornbeck Spiny lobster movement patterns 43 channel of the WSeR was poor through most of the present studies, rendering visual cues impossible except at very close range. during daylight, divers could often only distinguish objects up to 1 m away. A large patch reef would be visually lost within 5 m. odours and other chemical cues could be used when available, however, many daily tracks and forereef migrations were primarily north and south, which was at right angles to a general but inconsistent east-to-west current in Hawk channel (Smith & Pitts 1998). However, for daily tracks, chemical cues may provide "fine tuning" of movements to find food or specific shelters. Chemical cues also could be critically important when an individual lobster moves into unknown territory and finds itself downcurrent of a large patch reef with an aggregation of lobsters (Horner et al. 2006; Nevitt et al. 2000). Hawk channel is well inside the emergent reef of Western Sambo and, therefore, wave surge does not occur in this study area. although a weak eastto-west current may provide a means to create a chemical plume, this current reverses or comes to a standstill with the tides and certain wind conditions (R.d. Bertelsen pers. obs.). Much of the daily tracking data we generated with the pilot study grid strongly resembled and supported the findings of the Tektite-II project of the 1970s (cooper & Herrnkind 1971; Herrnkind & Mclean 1971; olsen et al. 1972; Herrnkind et al. 1975). Similar to the Tektite-ii project, we found repetitive daily paths to and from several possible foraging areas and we found that lobsters routinely used several patch reefs for shelter at a scale that can approach 1 km. Because this study did not use direct observations by diver surveys, we used patch reef switching as a proxy for den switching. However, it is not possible to know from our data if a given lobster returns to the exact same den on a given patch reef. as in the Tektite-ii project, we found great variation in movement profiles between individual lobsters with some individuals remaining close to their dens and others leaving the study site, although overall movement peaked after sunset and before sunrise. also, the Hawk channel spiny lobster generally slowed down and began to meander from about midnight to 0300 h. another palinurid, P. interruptus was recently tracked using acoustic tags and ScUBa observations moving on average from 250 m to 600 m in a linear manner (Hovel & lowe 2007) similar to the tracks we found for P. argus. Unlike P. argus, Hovel & Lowe (2007) report low site fidelity for P. interruptus. Reproductive migration Homing ability plays a role not only in the daily movements of P. argus, but also in the potential reproductive migrations of P. argus females. The early descriptions of reproductive migrations of P. argus in Florida keys viewed the process as season-long displacement where female lobsters left inshore waters for deeper waters to reproduced then returned once the season was over (dawson 1949; dawson & idyll 1951). later studies (davis 1974; lyons et al. 1981) supported this view. davis (1974) expanded this reproductive migration description to include the nearby dry Tortugas islands, which was subsequently supported by Bertelsen et al. (2000). These studies cited the changing of sex ratios to predominately male in inshore waters during this time as evidence for this migration (Bertelsen & Matthews 2001). However, in both 2003 and 2004, acoustic tagging of egg-bearing Hawk channel females revealed that these females consistently departed Hawk channel for the forereef or further and returned approximately 1 week later. The journey typically began near midnight and took approximately 2 nights. Multiple trips were detected for some individuals. None of the males we tagged appeared on the forereef during the reproductive season. We consider that the Hawk channel eggbearing females mate with Hawk channel males, because most of the egg-bearing females tagged had fresh spermatophores. The forereef migration of inshore female P. argus may therefore represent something of a "revolving door" that both enhances the number of females in offshore deeper waters and depletes their number in Hawk channel. Nomadism and emigration olsen et al. (1972) reported daily emigration of between 0.6 to 2.6% and 2.7% at two separate sites during the Tektite-ii project. This daily emigration rate extrapolates to approximately a 34% monthly rate of emigration of initial residents (i.e., excluding subsequent immigrants). They also reported that approximately 12% of those tagged returned after extended periods of time (between 20 and 74 days) (olsen et al. 1972). our estimated net emigration of 25% of males after 54 days compares well with their figure. We could not estimate female emigration as it was impossible to know during the tagging process whether a female was a local resident or non-local passing through the site at the time of tagging. one tagged female may have been a nonlocal lobster because it was not detected in the grid after tagging, but was detected by receivers placed

11 44 New Zealand Journal of Marine and Freshwater Research, 2009, Vol. 43 near the forereef during two occasions separated by approximately one month. Nomadic movements are more likely with immature lobsters (Herrnkind 1980) and during ontogenetic shifts (Childress & Jury 2006). Although our study was not conducted at a scale that could estimate rates of nomadism nor did we tag juvenile lobsters, the frequency of large daily shifts in location (>100 m) was greatest in small (<75 mm CL) female lobsters (>50%) and decreased in large ( mm CL) female lobsters (>25%). No clear pattern was found in daily shifts in location by size class of male lobsters. The frequency of greater movement in small females has also been shown for Jasus edwardsii: Kelly & MacDiarmid (2003) studying J. edwardsii movement patterns in New Zealand, found the number of days of site association (remaining within an approximately 15 ha reef) increased approximately linearly with female size. Large males also showed greater site association than small males, however, the increase was more of a step function occurring at 130 mm CL (Kelly & MacDiarmid 2003). Linnane et al. (2005) found that immature J. edwardsii females exhibited the greatest movement rates in South Australia. Heupel et al. (2006) reviewed different strategies of deployment of acoustic receivers with cost and benefit analysis of these deployment designs. One unexpected benefit we found regarding the initial use of an acoustic receiver grid, was that it provided valuable guidance for future larger-scale deployments of receivers. Such receivers would include gates and parallel curtains which are used to detect the passage of a tagged animal from one region to another (Heupel et al. 2006), and adjacent rings of receivers around habitats larger than patch reefs (e.g., emergent forereef s and deep water rocky outcroppings). For the classifications of movement patterns of lobster as elucidated by Herrnkind (1980) and Childress & Jury (2006), the grid strategy seems best suited for the study of daily and some homing activities. Curtains and gates are best suited for nomadic and migratory movements provided preliminary observations have been obtained to guide deployment. ACKNOWLEDGMENTS We gratefully acknowledge support from the Florida Keys National Marine Sanctuary (FKNMS) for permitting support and FKNMS and US Navy for boat dockage space. We also thank the following Florida Fish and Wildlife Conservation Commission staff for support in the field; P. Barbera, C. Cox, A. Dahood, D. Eaken, M. Feeley, J. Giganti, C. Lewis, T. Matthews, K. Maxwell, K. Miller, B. Sharp, J. Simonds, and M. Tellier. Also assisting in the field were FKNMS staffer S. Braynard and our tibervolunteer D. Hawtof. Research funded by grants from the EPA (X ) and NOAA (MOA ) REFERENCES Bertelsen RD, Hunt JH, Muller R Spiny lobster spawning potential and population assessment. A monitoring program for the South Florida fishing region. NOAA Final Report. FO p. Bertelsen RD, Matthews TR Fecundity dynamics of female spiny lobster (Panulirus argus) in a south Florida fishery and Dry Tortugas National Park lobster sanctuary. Marine and Freshwater Research. 52: Boles LC, Lohmann KJ True navigation and magnetic maps in spiny lobsters. Nature 421: Childress MJ, Jury SH Behaviour. In: Phillips BF ed. The biology of lobsters. Oxford, United Kindom and Ames, United States, Blackwell Publishing. Pp Cooper R, Herrnkind W Ecology and population dynamics of the spiny lobster, Panulirus argus, of St. John Island, U.S.V.I. In: Miller JW, Van Derwalker JC, Waller RA ed. Scientists in the sea. US Department of the Interior, Washington, DC. Pp Cox C, Hunt JH Change in size and abundance of Caribbean spiny lobsters Panulirus argus, in a marine reserve in the Florida Keys National Marine Sanctuary, USA. Marine Ecology Progress Series 294: Crawford DR, de Smidt WJJ The spiny lobster, Panulirus argus, of southern Florida: its natural history and utilization. Bulletin of the US Bureau of Fisheries 38: Davis GE Notes on the status of spiny lobsters Panulirus argus at Dry Tortugas, Florida. United States National Park Service report. US Department of the Interior, Washington DC, United States. 9 p. Dawson CE Florida crawfish research. Proceedings of the Gulf and Caribbean Fisheries Institute 1: Dawson CE, Idyll CP Investigations of the Florida spiny lobster, Panulirus argus (Latrielle). State of Florida, Board of Conservation, Technical Series No p.

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