Castro & Cobb—Behaviour of American lobstersResearch, 2005, Vol. 39: 963–972 New Zealand Journal of Marine and Freshwater 0028–8330/05/3904–0963 © The Royal Society of New Zealand 2005
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Behaviour of hatchery-reared and wild-caught 4th and 5th stage American lobsters, Homarus americanus
KATHLEEN M. CASTRO Department of Fisheries, Animal and Veterinary Sciences University of Rhode Island East Farm, Building 83 Kingston, Rhode Island 02881 United States email:
[email protected] J. STANLEY COBB Department of Biological Sciences University of Rhode Island Kingston, Rhode Island 02881 United States Abstract Behavioural deficiencies in 4th and 5th stage hatchery-reared lobsters were examined using time budget analysis and predator trials. Hatcheryreared 4th stage lobsters were found to behave differently than wild-caught lobsters and differences existed between hatchery-reared lobsters from different sources. Local hatchery-reared 4th stage lobsters spent less time on shelter and suffered higher predator rates in laboratory trials than both wildcaught 4th stage and lobsters reared in a hatchery in Maine. Fifth stage hatchery-reared lobsters spent significantly more time in shelter than their wildcaught counterparts. These differences may be attributable to the lack of development of proper predator-avoidance behaviour and need to be understood and corrected to maximise the effect of enhancement projects. Keywords Homarus americanus; hatcheryeffects; predator-prey; time budgets; behaviour; post-settlement processes
M04108; Online publication date Received 11 May 2004; accepted 10 March 2005
INTRODUCTION There are many factors that influence the success of marine stock enhancement projects, including environmental conditions, population interactions, and the quality of the animal produced by the hatchery. The physiological, morphological, and behavioural characteristics of the animal can greatly influence the ultimate fate once released into the natural environment (Olla et al. 1998). To optimise survival and growth, hatchery-reared animals are maintained in predator-free conditions, fed highly nutritional feed, and kept under ideal rearing conditions. Individuals are maintained separately with no physical contact if they are cannibalistic. An animal reared in this environment may develop abnormal behaviour or fail to develop normal behaviours needed for survival in the natural environment (Blaxter 1976; Olla et al. 1995). Morphologically and physiologically, 4th and 5th stage hatchery-reared American lobsters (Homarus americanus) differ from wild-caught lobsters. They are smaller, have weaker exoskeletons, are lighter in colour, swim more slowly, and have reduced growth rates (Lavalli 1991; Rooney & Cobb 1991; Juinio & Cobb 1994; James-Pirri 1996; James-Pirri & Cobb 1997; James-Pirri et al. 1998). General hatchery protocol for rearing Homarus uses Artemia that can be enriched using plankton or artificial enrichers (Super Selco). Although moult-related mortality is high on this feed, there is no substitute that is economically available for commercial hatchery use. In a recent study (Castro et al. 2000), over 6000 micro-wire tagged hatchery-reared 5th and 6th stage lobsters were released onto artificial reefs in Narragansett Bay, Rhode Island, United States. Only three of these were recovered after intense sampling within 1–3 weeks, indicating a low survival probability. We hypothesised that behavioural abnormalities led to high predation rates, but it is unknown how behaviour of lobsters may be affected by hatchery-rearing conditions. This study examined the time budgets of hatchery-reared and wild-caught 4th and 5th stage lobsters, and ultimate survival rates for 4th stage lobsters in predation trials.
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METHODS AND MATERIALS General laboratory set-up, rearing and field collection Lobsters were maintained in two recirculating systems that were equipped with a settling tank, mechanical filters, U/V sterilisation, biofilter, and chiller. Systems were in a room with a reverse light cycle (12D:12L). Artificial sea water (Crystal Sea Marinemix, Marine Enterprises International, Baltimore, Maryland, United States) was mixed to a salinity of 28–30 psu and maintained at 16–18°C. Predators (cunner, Tautogolabrus adspersus) were held in a separate recirculating system. Wild-caught lobsters Wild 4th stage lobsters were collected on 30 June 2000 and on 26 June and 10 July 2001 using plankton nets during routine sampling in Block Island and Rhode Island Sound. Upon capture, lobsters were immediately placed in vials containing salt water and held in a cooler with ice. They were slowly acclimated to tank temperature before transfer to individual 25 mm diameter PVC containers in the recirculating systems. All wild 5th stage lobsters tested in future experiments were 4th stage lobsters captured and held in the laboratory. Hatchery-reared lobsters Female brooders were obtained from Rhode Island fishers in the spring, and maintained in recirculating systems with a reverse light-dark cycle to allow for collection of larvae during the day (Aiken & Waddy 1995). First stage larvae were collected daily (June– August), in an overflow system and transferred to standard Hughes air driven upweller tank systems (Hughes et al. 1974; Beal et al. 1998). Lobster larvae were maintained at an average density of 15 animals per litre and fed live Artemia nauplii (density of 25 animals/ml) until metamorphosis. Artemia were hatched from eggs (Aquatic Ecosystems) and maintained on cryo-perserved algae paste (Instant Algae (Isochrysis and Chaetoceros), Reed Mariculture, San Jose, California, United States). After metamorphosis, the 4th stage lobsters were transferred to individual PVC containers placed in recirculating systems and fed frozen adult Artemia daily. Additional 4th stage lobsters were obtained from the Mt. Desert Oceanarium Lobster Hatchery in Southwest Harbor, Maine on 18 August 2000 and 1 August 2001. Larval rearing at the Mt. Desert facility was similar to that used at the University of Rhode Island, except that filtered salt water was obtained
from the natural environment and maintained at cooler temperatures. Larval lobsters were fed live Artemia. The lobsters were transported on moist paper in coolers with ice packs (6 h) and immediately placed into individually numbered PVC containers in the recirculating system with artificial sea water as explained above. Time budget analysis Time budget analysis was used to evaluate general behaviour of hatchery-reared and wild-caught 4th and 5th stage lobsters (Lawton 1987). Fifth stage behaviour was examined in 2000; 4th stage time budget and predation trials were run in 2001. For all experiments, lobsters were food-deprived 12–24 h before the start of the experiment. Observations were made under dark conditions using red lights. Individual lobsters were placed in a small plastic container (135 ¥ 135 mm; 50 mm height) with a patch of cobble and a PVC shelter in one corner. The remainder of the bottom was featureless. The observation period started 15 min after the lobster was placed in the container, when a small food source was added (piece of mussel mixed with Artemia) into the opposite corner. The lobster was observed for 15 min and each predefined behaviour was recorded. Defined mutually exclusive behaviours were: sheltering (lobster was in physical contact with the cobble or with the actual shelter provided); exploring (lobster left physical contact with cobble area; either immobile or moving); feeding (lobster handled food provided). Two observers conducted the behavioural analysis. To reduce observer bias, behavioural observations were conducted together until there were minimal discrepancies between observers (±1 s). Each trial was analysed for time spent in each behaviour (sheltering, exploring, or feeding). Time budgets were constructed by summing the duration of discrete units of activity patterns and determining the proportion of time spent in each behaviour. Proportions were transformed using the Arcsin square root transformation (Sokal & Rolff 1980) and tested for normality, independence, and homogeneity of variances. The transformed data were analysed for differences in mean time spent on shelter using a one-way ANOVA and multiple comparisons were evaluated using the Tukey studentised range post hoc test (SAS 8.1; Cody & Smith 1997). A contingency table analysis was used to compare the proportion data from each behaviour category (Zar 1999). The time budget analysis for the 4th stage lobsters was conducted from 25 June to 13 August 2001.
Castro & Cobb—Behaviour of American lobsters There were 45 URI hatchery-reared, 49 Maine hatchery-reared, and 45 wild-caught lobsters observed in this experiment. Lobsters were used once. Time between metamorphosis and testing was standardised to test animals in the same stage of the moult cycle. The wild-caught 4th stage lobsters were tested 0–6 days after capture; Maine hatchery-reared lobsters were tested 2–6 days after arrival, and URI hatchery-reared lobsters were tested 1–3 days after metamorphosis. However, because of the varying ages (moult stages) when first obtained, the days since metamorphosis were adjusted using known development rate data (James-Pirri et al. 1998). Three days were added to the wild-caught lobsters. Maine hatchery-reared lobsters were corrected by one day and URI hatchery-reared lobsters were left as recorded. The following hypothesis was tested. HØ: There is no difference in mean time spent on shelter between 4th stage lobsters from different sources. Time budget experiments for 5th stage lobsters were conducted from 28 June to 18 September 2000. Animals were used 3–4 days after moulting from 4th stage (lobsters were used once) to standardise moult stage (n = 32 wild lobsters; n = 24 URI, and n = 21 Maine hatchery-reared lobsters) to test the following hypothesis. HØ: There is no difference in mean time spent on shelter between 5th stage lobsters from different sources. Predator trials After the time budget trial, 116 of the 4th stage lobsters (year 2000) were used immediately in predation trials. Nine aquariums were supplied with a continuous airflow and filled with 37.8 litres of artificial sea water with a salinity of 29 psu and maintained at 16–18°C . The aquariums were set up with a small substrate area that consisted of white deco pebbles, small rocks, and oyster shells. The remainder of the bottom was featureless. Aquariums were placed in a room with a reversed 12L:12D cycle. One 4th stage lobster was introduced into each aquarium (staggered by 15 min) during the dark cycle and acclimated for 24 h with a caged fish predator (cunner). At the end of the 24 h period, the cunner was released from the cage. Behavioural observations were made under red light for the first 15 min (time period 1), the first 5 min of hour 2 (time period 2), and hour 3 (time period 3). A final observation made after 24 h was only to determine if the lobster had survived. Differences in survival after the 24 h interval were determined using binary regression analysis (SAS, Proc GENMOD) using
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Fig. 1 Mean proportion of time spent on shelter (error bars = standard error) for the three sources of 4th and 5th stage lobsters in the time budget trials (n = total number tested). (URI, University of Rhode Island.)
maximum likelihood estimation (Allison 1999). The independent variable (source) was treated as categorical data whereas the dependent variable (dead or alive) was binomial (LOGIT model for 3 ¥ 2 table). The quality of fit from generalised linear models was determined from the scaled deviance statistic that had a distribution similar to a chi-square. Chi-square values are therefore reported for significance testing (Allison 1999). RESULTS There were significant differences in the mean time spent on shelter for 4th stage lobsters between sources (P = 0.0001; F = 22.8; d.f. = 2) (Table 1). The URI hatchery-reared lobsters spent significantly less time on shelter (25%) than either Maine hatchery-reared (68.5%) or wild-caught lobsters (71%) (Fig.1). There was no difference between the two sources of hatchery-reared 5th stage lobsters but wild-caught 5th stage lobsters spent significantly less time on shelter than either of the hatchery-reared lobsters (F = 14.7; P = 0.0001; d.f. = 2) (Fig. 1, Table 1). As a result of the correction for age/moult stage (Fig. 2) only one day (day 3) was available as a direct comparison among sources for 4th stage lobsters. There was a significant difference in time spent on shelter between URI hatchery-reared and the Maine hatchery-reared and URI hatchery-reared and wild-caught lobsters (Table 2, F = 10.9, P = 0.0002, d.f. = 2). Behavioural time budgets for 4th stage lobsters were not independent of the source of lobsters
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New Zealand Journal of Marine and Freshwater Research, 2005, Vol. 39 Fig. 2 Mean proportion of time spent on shelter by source of 4th stage lobster according to days lapsed since metamorphosis (error bars = standard error; n = total number of lobsters tested). (URI, University of Rhode Island.)
Table 1 Effects of source on use of shelter in 4th and 5th stage lobsters using an analysis of variance and Tukey’s post hoc comparison. (URI, University of Rhode Island.) Source 4th stage Model Error Corrected total 5th stage Model Error Corrected total
d.f.
SS
MS
F
P
2 83 85
7.125 12.954 20.079
3.562 0.1561
22.83
