Patrick Ouellet

AN INVESTIGATION OF THE SOURCES OF VARIABILITY IN AMERICAN LOBSTER (HOMARUS AMERICANUS) EGGS AND LARVAE: FEMALE SIZE AND REPRODUCTIVE STATUS, AND INTERANNUAL AND INTERPOPULATION COMPARISONS

Abstract From 1997 to 2001, the effects of female size (cephalothorax length [CL]) and reproductive status on egg size (diameter, dry weight) and larva CL at hatching were investigated in two Homarus americanus populations in the Gulf of St. Lawrence (Îles-de-la-Madeleine, Anticosti) and one at Grand Manan (Bay of Fundy), Canada. The estimated size at 50% maturity was used to identify small (likely primiparous) females for each population. Multifactor, mixed-hierarchical ANOVA models were used to investigate the variability of eggs and stage I CL among years and populations. In all comparisons, the main source of variability in the egg and stage I larva size was females (within and among). Nevertheless, for the Îles-de-la-Madeleine population in each year except 2001, the mean stage I larva sizes from small (CL < 79 mm), probably primiparous females were significantly smaller (P < 0.0085) than the mean larva sizes from larger females. However, female CL per se explained very little of the variance in mean larval size at hatching (r2 = 0.23, P < 0.05 and r2 = 0.12, P = 0.22 in 2000 and 2001, respectively, when the entire size range of reproductive females was considered). Hatching larvae tend to be smaller in primiparous females or females maturing at a small size; however, over the entire size range of reproductive females, larval size at hatching is almost independent of female size (CL). It is as if, above a minimum viable size, there is a constant small range of egg/larval sizes produced in H. americanus. Conservation measures dealing with the imposition of a minimum legal size may be a means of increasing the number of females that will spawn at least once or twice within a population. However, the impacts of first-time spawning on quality of eggs and larvae need to be fully investigated to assess the response of the populations egg production and recruitment potential of this measure.

Effect of temperature on development rate of larvae from cold-water American lobster (Homarus americanus)

The duration of the larval phase of the American lobster influences the distance larvae drift, and thus the potential settlement and recruitment patterns of lobsters to local populations and fisheries. The duration of larval stages is influenced by temperature, with warmer temperatures resulting in faster development and shorter stage duration. The quantitative relationship between temperature and duration of larval stages has been previously investigated, but only for lobsters originating from relatively warm-water regions. We examined the effects of temperature on stage duration for lobster larvae originating from a cold-water region, the northern shore of the Gaspe Peninsula in the northern Gulf of St. Lawrence, Canada. We reared larvae individually using a new experimental apparatus with automated movement of culture containers to facilitate water exchange. We compared observed duration of larval stages for these cold-water source larvae to durations in previous studies that used warmer-water source larvae. We observed 38% shorter development times at the coldest temperature used (10°C) and 47, 50, and 100% longer development times at warmer temperatures (14, 18 and 22°C, respectively) than at the same temperatures in previous studies of warm-water larvae, suggesting potential geographic variation in the functional relationship between temperature and larval development time. Given these results, future research should examine this question in more detail, to enhance understanding of lobster ecology and population dynamics across the species’ range.

EGG DEVELOPMENT TRAJECTORIES OF EARLY AND LATE-SPAWNER LOBSTERS (HOMARUS AMERICANUS) IN THE MAGDALEN ISLANDS, QUEBEC

Abstract This study examines egg development in American lobster (Homarus americanus) ovigerous females caught off the Magdalen Islands (MI), Québec, in September 2002 and kept in tanks for 10-11 months under a simulated natural temperature cycle. The study compares egg development trajectories of 7 early-spawners (ES) that had a well-defined pigmented eye area (Perkins eye index, PEI: 190-246 µm) at the time of capture and 8 late-spawners (LS) with no visible pigmented eye at the time of capture. Eggs from ES achieved about 80% of their development in the fall, followed by a circa 6-months rest period. Eggs from LS reached approximately 50% development by late fall, and unlike eggs from ES, continued development during winter even at temperatures of 1.0-1.5°C. The two groups experienced different numbers of effective (> 3.4°C) degree-days (ES: 1440.7, LS: 1308.0) for complete embryonic development and late spawning translated into late hatching. Additional observations made on a group of 72 ovigerous MI females caught in September 2006 indicate that early spawning is mainly associated to larger females, most likely multiparous, with a 2-year reproductive cycle, and late spawning mainly to smaller females, most likely primiparous, with a 1-year cycle, molting and spawning the same year. Larvae from ES/multiparous and LS/primiparous may therefore encounter different environmental conditions for survival at hatching and during larval development. The occurrence of females having different patterns of egg development trajectories in American lobster populations can help spread larval production over time. This can be viewed as a mechanism for coping with environmental uncertainty.

Diet Components of Northern Shrimp Pandalus Borealis First Stage Larvae in the Northwest Gulf of St. Lawrence

Abstract The objective of this study was to clarify the diet composition of the first stage larvae of northern shrimp Pandalus borealis during the spring period of high biological production in the Northwestern Gulf of St. Lawrence (NWGSL). Data collected in spring 2006 revealed that hatching of P. borealis larvae took place in late April and early May during a period characterized by a phytoplankton bloom (mainly species of the genus Chaetoceros) and by an abundance of early stages of mesozooplankton, which demonstrated the onset of secondary production at the sampling site. Gut content examination of stage I larvae sampled at the site and feeding experiments conducted at sea revealed that omnivorous feeding starts at hatching, but a first approximation based on the quantity of pigments present in the larvae suggest that zooplankton is more important than phytoplankton to meet the larvaes energy needs. In addition, field observations of the degree of gut fullness and the low percentage (10%) of larvae with empty guts indicate a high feeding success. Hatching at the time of production of adequate prey could represent a major factor for larval northern shrimp survival in the NWGSL.

Vertical distribution of snow crab (Chionoecetes opilio) pelagic stages in the Gulf of St. Lawrence (Canada) and effect of temperature on development and survival

Knowledge of the vertical distribution, thermal habitat, and growth of the larvae of the cold stenothermic snow crab (Chionoecetes opilio) is incomplete and inconsistent. This study explored aspects of the vertical distribution and development rate of larvae from eastern Canada. In the Gulf of St. Lawrence (GSL), during 2002, the mean vertical positions of the snow crab zoeae I and II larvae were recorded within and above the permanent thermocline and in close association with the depth of strong density discontinuities in the stratified water column. No statistically significant differences were detected between nighttime and daytime vertical positions. The water temperatures at the centre of the larvae distributions were 2–3 C in late May in the colder northern GSL and 7–8 C in June in the warmer southern GSL. Data from the literature and from a rearing experiment in 2014 were used to develop functions linking development and survival to water temperature. Assuming the snow crab larvae remain in the upper mixed layer until final metamorphosis, development may last 2.2–4 months depending on hatch time and location. Development would be prolonged by several weeks if premolt megalopae move into and reside in the deeper, colder waters as appears to be the case. A relative survival index suggests that optimum temperature for development is around 10.8 C, 9.5 C, and 8.7 C for snow crab zoea I, zoea II, and megalopa, respectively. These results should contribute to modelling efforts that aim to evaluate the extent of larval drift and location of potential settlement areas, as well as the potential impact of climate change on snow crab in the North Atlantic.