Improvement of larval rearing technique for mass seed production of snow crab <Emphasis Type="Italic">Chionoecetes opilio</Emphasis>

Larval rearing experiments were conducted to examine the potential for mass seed production of the snow crab Chionoecetes opilio using a total of eight 20-kL tanks. Tanks were equipped with agitators, which move the water using a rectangular blade to prevent the zoeas sinking to the bottom of the tank. Larval rearing water was treated with sodium nifurstyrenate once a week to reduce the chance of larval infection by pathogenic bacteria. Zo eas were fed with rotifers and Artemia nauplii. A total of 122 830 megalops and 16 660 first-stage crabs were produced. Thus, the potential for mass seed production of snow crab was determined. Survival rates up to the megalopal stage were high in tanks with a feeding regime that fed rotifers to larvae through an entire zoeal stage. This study also describes the fatty acid composition of snow crab larvae. It revealed that the first zoeas had a high DHA content and DHA/EPA ratio, but these values significantly decreased in the second stage zoeas and megalops. Improving the DHA content and/or DHA/EPA ratio of larvae should be important in studies on mass seed production technology of the snow crab.     

Use of reflex indicators for measuring vitality and mortality of the snow crab (Chionoecetes opilio) in captivity

The snow crab (Chionoecetes opilio) is one of the most important commercial crabs in the world; it is heavily exploited in Atlantic Canada, Alaska, the Sea of Japan and the Barents Sea. Catches in the Barents Sea north of Norway have increased dramatically in the last decade. Most of the world's catch is processed, frozen and exported overseas. However, recently there has been considerable interest in exporting live snow crab, particularly in Norway. The stress of capture and live transport can result in significant mortalities. In order to establish a live export industry for snow crab, the welfare of the animal must be monitored throughout all the steps of the live transport process. In this study the reactions of snow crabs exposed to increasing periods of air exposure were measured in terms of reflex indicators, incidence of mortality, blood lactate levels and blood protein and haemocyanin. Although this is not a specific live holding or live transport process the aim was to test the suitability of reflex indicators to reflect vitality (stress) and not just to predict mortality. This would be compared with traditional blood biochemistry techniques for measuring crustacean stress. The study demonstrated that the reflex index score (RIS) is suitable to assess the vitality of snow crab. Longer air exposure periods render higher mortality rates and less vital individuals. The authors believe using vitality reflex indicators would be a suitable way of measuring crab welfare during the live holding and transport process.     

Long‐term trends and drivers of larval phenology and abundance of dominant brachyuran crabs in the Gulf of St. Lawrence (Canada)

Climate change has led to major shifts in the timing of biological events, with many studies demonstrating earlier phenology in response to warming. However, few of these studies have investigated the effects of climate change on the phenology of larvae in marine species. Phenological shifts can result in mismatches between consumers and prey and hence affect growth and survival of individuals, and ultimately population demography. We investigated the temporal changes in phenology and abundance of the larvae of dominant brachyuran crabs in the southern Gulf of St. Lawrence (eastern Canada) based on plankton collections spanning 1982–2012. The Gulf of St. Lawrence has warmed since the early 1990s, and our analyses revealed that larvae of snow crab (Chionoecetes opilio) and toad crabs (Hyas spp.) exhibited a significant trend towards earlier phenology over the 30‐year study period. This shift in phenology appeared to be a consequence of the effect of climate warming on both the timing of hatching and larval development rate. Larval abundance responded differently by crab taxon to climate warming, likely due to differences in thermal tolerance. The warming trend was unfavourable to snow crab, which is the most cold‐adapted and stenothermic of the taxa examined in this study. The abundance of snow crab larvae was lower when sea ice retreat occurred earlier than day 110 of the year and sea surface temperature was higher than 8.5°C. On the other hand, larval abundance of rock crab (Cancer irroratus), which prefers higher temperatures, was positively related to surface temperature.     

Links between the recruitment success of northern European hake (Merluccius merluccius L.) and a regime shift on the NE Atlantic continental shelf

The distribution of northern European hake (Merluccius merluccius L.) extends from the Bay of Biscay up to Norwegian waters. However, despite its wide geographical distribution, there have been few studies on fluctuations in the European hake populations. Marine ecosystem shifts have been investigated worldwide and their influence on trophic levels has been studied, from top predator fish populations down to planktonic prey species, but there is little information on the effect of atmosphere–ocean shifts on European hake. This work analyses hake recruitment success (recruits per adult biomass) in relation to environmental changes over the period 1978–2006 in order to determine whether the regime shift identified in several abiotic and biotic variables in the North Sea also affected the Northeast Atlantic shelf oceanography. Hake recruitment success as well as parameters such as the sea surface temperature, wind patterns and copepod abundance changed significantly at the end of the 1980s, demonstrating an ecological regime shift in the Northeast Atlantic. Despite the low reproductive biomass recorded during the last decades, hake recruitment success has been higher since the change in 1989/90. The higher productivity may have sustained the population despite the intense fishing pressure; copepod abundance, warmer water temperatures and moderate eastward transport were found to be beneficial. In conclusion, in 1988/89 the Northeast Atlantic environment shifted to a favourable regime for northern hake production. This study supports the hypothesis that the hydro‐climatic regime shift that affected the North Sea in the late 1980s may have influenced a wider region, such as the Northeast Atlantic.     

Effect of starvation on the survival,injury, and weight of adult snow crab,Chionoecetes opilio

In this study, the effects of feeding (F) and starvation (S) on survival, injury, and weight of captive male snow crab were examined. The experiment was carried out with three replicates of each treatment. Each replicate had 11 individually tagged crabs (average weight of 650 g ± 37 SE) per tank (replicate) in a total of six circular tanks (500 L), with stocking densities of 14 kg/m. The experiment ran for 100 days and the animals were exposed to ambient seawater temperatures ranging from 4.4ºC to 5.4ºC during the trial period. There were no significant differences in wet weight between the groups at the start or at the end of the experiment. However, the hepatopancreas index (HI) significantly decreased in both groups from 6.1% at the start to, respectively, 4.6% (F) and 3.2% (S) at day 100. The S group had a significantly lower HI than the F group. Only one animal died during the experiment (day 100, F). The frequencies of injuries were similar in all groups. The results show that adult male snow crab can be stored for minimum 100 days (with or without feeding) with relatively low risk of physical injury, or mortality due to social interactions.     

Tissue distribution of hepatopancreatic parvo‐like virus of shrimp in freshwater rice‐field crab,Paratelphusa hydrodomous (Herbst)

An attempt was made to determine the replication efficiency of hepatopancreatic parvo‐like virus (HPV) of shrimp in different organs of freshwater rice‐field crab Paratelphusa hydrodomous (Herbst) using bioassay, PCR, RT‐PCR, ELISA, Western blot and q‐PCR analyses. Another attempt was made to use this crab as an alternative to penaeid shrimp for the large‐scale production of HPV. This crab was found to be highly susceptible to HPV by intramuscular injection. The systemic HPV infection was confirmed by PCR and Western blot analyses in freshwater crab. The expression of capsid protein gene in different organs of infected crab was revealed by RT‐PCR analysis. Indirect ELISA was used to quantify the capsid protein in different organs of the crab. The copy number of HPV in different organs of the infected crab was quantified by q‐PCR. The results revealed a steady decrease in C_T values in different organs of the infected crab during the course of infection. The viral inoculum that was prepared from different organs of the infected crab caused significant mortality in post‐larvae of tiger prawn, Penaeus monodon (Fabricius). The results revealed that this rice‐field crab could be used as an alternative host for HPV replication and also for large‐scale production of HPV.     

High efficacy of white spot syndrome virus replication in tissues of freshwater rice‐field crab,Paratelphusa hydrodomous (Herbst)

An attempt was made to determine the replication efficiency of white spot syndrome virus (WSSV) of shrimp in different organs of freshwater rice‐field crab, Paratelphusa hydrodomous (Herbst), using bioassay, PCR, RT‐PCR, ELISA, Western blot and real‐time PCR analyses, and also to use this crab instead of penaeid shrimp for the large‐scale production of WSSV. This crab was found to be highly susceptible to WSSV by intramuscular injection. PCR and Western blot analyses confirmed the systemic WSSV infection in freshwater crab. The RT‐PCR analysis revealed the expression of VP28 gene in different organs of infected crab. The indirect ELISA was used to quantify the VP28 protein in different organs of crab. It was found that there was a high concentration of VP28 protein in gill tissue, muscle, haemolymph and heart tissue. The copy number of WSSV in different organs of infected crab was quantified by real‐time PCR, and the results revealed a steady increase in copy number in different organs of infected crab during the course of infection. The viral inoculum prepared from different organs of infected crab caused significant mortality in tiger prawn, Penaeus monodon (Fabricius). The results revealed that this crab can be used as an alternate host for WSSV replication and production.     

A model to explain the formation of catarina scallop, Argopecten circularis (Sowerby, 1835), beds, in Magdalena Bay, Mexico

Abstract. During the years of 1989 and 1990, the yield of the commercial fishery for the catarina scallop, Argopecten circularis (Sowerby, 1835), in Magdalena Bay, was 750 million organisms (5186t of muscles), which were gathered by diving at 12–30m depth. This production is the largest registered to date and accounted for 53% of the total Mexican scallop production since 1981. The formation of large beds in that area is a sporadic phenomenon which needs to be studied. In the present paper, a model to explain the formation of such beds is drawn, in which the bentho-pelagic red crab, Pleuroncodes planipes (Stimpson, 1860), plays a role as primary substrate for the recruitment of the spat and simultaneously is the active transporter of juveniles into the Bay during the winter months of cold years. Apparently exploitable beds are formed only when temperatures of 16°C or lower, are registered deep inside the Bay for at least 2 months. Relating these findings with short and long-term temperature fluctuations, it seems possible to predict future exploitable stocks in the area.     

Contrasted optimal environmental windows for both sardinella species in Senegalese waters

We investigate Sardinella aurita and Sardinella maderensis recruitment success relative to the variability of oceanographic conditions in Senegalese waters using generalized additive models (GAM). Results show that recruitment of both species is marked by a strong intra‐annual (seasonal) variation with minimum and maximum in winter and summer, respectively. Their interannual variations are synchronous until 2006 (recruitment decreasing), while from 2007 there is no synchrony. The model developed shows that sardinella recruitment variability is closely related to the tested environmental variables in the study area. However, the key environmental variables influencing the recruitment success are different for both species: the Coastal Upwelling Index and the sea surface temperature for S. aurita and S. maderensis, respectively. We report that recruitment success of S. aurita and S. maderensis are associated with distinct ranges of sea surface temperature, upwelling intensity, wind‐induced turbulence, concentration of chlorophyll‐a and north Atlantic oscillation index. Considering food security and socio‐economic importance of both stocks, we recommend that consideration is given to the environmental variability in the small pelagic fish national management plans, particularly in the context of climate change.     

Holding wild Snow crab,Chionoecetes opilio: effects of stocking density and feeding on survival and injury

In this study the effects of different stocking densities on survival, injury and weight of captive male snow crab were examined. The first experiment (I) was carried out in square plastic tanks (700 L) with stocking densities of 100 (L), 150 (M) and 200 kg m^?3 (H) for 30 days. In a second experiment (II) snow crabs were kept at a stocking density of 50 kg m^?3 and were either fed (F) or not fed (S) for the same period of 35 days. The last experiment (III), was carried out with stocking densities of 25 kg m^?3 for 21 days with two groups, one with inactivated claw and one without rubber bands, with three replicates per treatment. In the first experiment mortality (H = 27, M = 26 and L = 36%) and occurrence of injuries (H = 27, M = 20 and L = 16%) were high in all groups. The weight loss during the experimental period was; H = 15.3, M = 10.9 and L = 15.5 g, and was not significant different between the groups. In experiment II the mortality (F = 13% and S = 14%) and injuries were lower (F = 12% and S = 17%). The average weight increased in the fed treatment and decreased in the starved treatments. In the last experiment there was no mortality in any of the groups and the levels of injury were low (5% and 7%). The results show that adult male snow crab cannot be stored at densities equal to or higher than 25 kg m^?3 for 3 weeks without risk of mortality.     

Development of performance indices for the Newfoundland and Labrador snow crab (Chionoecetes opilio) fishery using data from a vessel monitoring system

This study investigates the potential for using data from a vessel monitoring system (VMS) to create indices of commercial fishery performance that may be used in monitoring snow crab resource status. Fishing hours were screened from hourly positional signals to create an index of fishing effort (hours fished) for comparison with that derived from logbooks (number of trap hauls). Similarly, a VMS-based fishing catch per unit of effort (CPUE) index was developed for comparison with CPUE derived from logbooks. Analysis of these indices showed that VMS-based fishing effort and CPUE indices can be interpreted to provide reliable complementary or alternative indices to logbooks for assessment of fishery performance in the Newfoundland and Labrador (NL) snow crab (Chionoecetes opilio) fishery. We also developed a VMS-based index of fishing efficiency and illustrate how it can be applied toward understanding various behaviors and anomalies in the fishery. VMS data may offer other potential applications for snow crab assessment and management. Our approach and methods are applicable to other commercial fishery resources worldwide that are monitored using vessel monitoring systems.     

Unintended consequences of climate-adaptive fisheries management targets

Climate change is projected to affect the productivity of global fisheries. Management based on maximum sustainable yield (MSY) has been effective at eliminating overfishing in many regions. However, continuing to use yield-maximizing targets under climate-driven changes in productivity can result in higher anthropogenic pressure on populations subject to climate-related stress than maintaining status quo management targets. We demonstrate this effect using a theoretical example and case studies from snow crab in the eastern Bering Sea and a global marine fisheries database. In these examples, the conservation gain (i.e. biomass in the ocean) of maintaining status quo management targets is larger than the small gain in harvest made through climate adaptation in MSY-based management. The aggregate conservation gain of maintaining management targets increases as the harmful impacts of climate change on productivity worsen. Instead of climate-adaptive MSY-based targets, new management tools are needed to balance conservation and food production in ecosystems of populations displaying non-stationary productivity.     

Effects of dietary protein sources on growth,survival and digestive capacity of Octopus maya juveniles (Mollusca: Cephalopoda)

We propose two hypotheses to explain the inexistence of adequate prepared diet for Octopus maya at this date: Hypothesis 1 is related to changes in protein structure during protein cooking, which affects the digestibility. Hypothesis 2 is related to changes on nutritional characteristics during ingredient process, which affects the nutritional composition of diet. To test hypothesis 1, experiments one and two were directed to determine if protein cooking reduces digestibility and growth of animals when compared to fresh or lyophilized protein sources. For hypothesis 2, three experiments were conducted, testing seven different dietary protein sources offered in isolation or combined in artificial diets fed to O. maya. Results demonstrated that the diets that promoted growth were the ones based on fresh crab paste, and both lyophilized crab and squid tentacles paste. In consequence hypothesis 1 was accepted. The cooking process also changed nutritional characteristics of protein sources, affecting the growth of O. maya. Results obtained when squid and crab were mixed suggest that nutritional requirements of octopuses were covered with that diet in similar forms compared to when using fresh or lyophilized crab, also confirming hypothesis 2. Based on growth rates obtained, we can conclude that nutritional requirements of O. maya must be between 80% and 86% Protein (P), 5.1–5.6% Lipids and a protein: energy ratio between (P/E) 38.9 and 42.2 g MJ^?1.     

Copepod dynamics across warm and cold periods in the eastern Bering Sea: Implications for walleye pollock (Gadus chalcogrammus) and the Oscillating Control Hypothesis

Differences in zooplankton populations in relation to climate have been explored extensively on the southeastern Bering Sea shelf, specifically in relation to recruitment of the commercially important species walleye pollock (Gadus chalcogrammus). We addressed two research questions in this study: (i) Does the relative abundance of individual copepod species life history stages differ across warm and cold periods and (ii) Do estimated secondary production rates for copepods differ across warm and cold periods? For most copepod species, warmer conditions resulted in increased abundances in May, the opposite was observed in colder conditions. Abundances of smaller‐sized copepod species did not differ significantly between the warm and cold periods, whereas abundances of larger‐sized Calanus spp. increased during the cold period during July and September. Estimated secondary production rates in the warm period were highest in May for smaller‐sized copepods; production in the cold period was dominated by the larger‐sized Calanus spp. in July and September. We hypothesize that these observed patterns are a function of temperature‐driven changes in phenology combined with shifts in size‐based trophic relationships with primary producers. Based on this hypothesis, we present a conceptual model that builds upon the Oscillating Control Hypothesis to explain how variability in copepod production links to pollock variability. Specifically, fluctuations in spring sea‐ice drive regime‐dependent copepod production over the southeastern Bering Sea, but greatest impacts to upper trophic levels are driven by cascading July/September differences in copepod production.     

Pacific herring (Clupea pallasii) consumption by marine birds during winter in Prince William Sound,Alaska

Following the 1989 MV Exxon Valdez oil spill (EVOS) and subsequent herring population collapse in Alaska's Prince William Sound (PWS), the Pacific herring (Clupea pallasii) fishery was closed. In the 25 yr since EVOS, herring and several herring‐dependent marine bird species have failed to reach pre‐spill population levels. One hypothesis is that intense predation pressure may be inhibiting herring recovery. To inform herring modeling efforts, this study estimated marine bird consumption of juvenile and adult herring in PWS for 10 winters over an 18‐yr period (1989–90 through 2006–2007). Total estimated herring consumption by wintering marine birds averaged 2409 ± 950 t, indicating that avian consumption represents a substantial and inter‐annually variable source of herring mortality. Common murre (Uria aalge) consumed the greatest portion (16–80%) of herring in all years among marine bird species. Juvenile herring biomass consumed annually by common murre was greater than murre consumption of adult herring biomass. Time lag analyses showed that marine bird consumption of adult herring is negatively correlated with the amount of herring spawn observed in subsequent years, but such effects were not observed more than 2 yr. Our models indicate that during years in which herring recruitment is low or bird populations are particularly large, marine birds can consume up to 10% of the annual adult herring biomass. Our results highlight the importance of herring to wintering PWS birds. We propose that future management of herring stocks seeks to reduce negative impacts on marine birds that prey on herring.     

Index‐based analysis of climate change impact on streamflow conditions important for Northern Pike,Chub and Atlantic salmon

Climate change is expected to affect the flow regime, cause loss of habitat, change community composition and behavioural habits of fish. This study assessed the impact of climate change on ecologically relevant streamflow conditions for fish migration and spawning in the Vistula and the Odra river basins. Streamflow simulations obtained with the Soil and Water Assessment Tool (SWAT) for the historical period and two future horizons were driven by nine bias‐corrected EURO‐CORDEX Regional Climate Models under two greenhouse gas concentration trajectories. This study identified a subset of Indicators of Hydrological Alteration (IHA) that are relevant for pike, Esox lucius L., chub, Squalius cephalus (L.), and Atlantic salmon, Salmo salar L. IHA indicators were calculated and compared for different scenarios. An index‐based framework identified that all considered species will be impacted by climate change, with Atlantic salmon facing the largest impact. The model's uncertainty was addressed through an aggregation method that assessed inconsistencies in the model's response.     

Activities of digestive enzymes in relation to ingested natural food in three carp species of the Himalayan River Ladhiya,northern India

The present investigation was carried out to study gut content and accompanying digestive enzyme profiles of the three carp species, golden mahseer Tor putitora, snow trout Schizothorax richardsonii and hill trout Barilius barila. The fishes were captured from the River Ladhiya, Champawat district, Uttarakhand, northern India. The digestive tract length was on average 1.8 and 2.3 times longer than the body, while members of Bacillariophyceae, Chlorophyceae, Cyanophyceae and Zygnematophyceae made up 95.15% and 99.63% of gut content in the golden mahseer and snow trout, respectively. In hill trout, the digestive tract being only half the body length, gut content was insects (72.73%), eggs of aquatic organisms (22.73%) and nematodes (4.55%). Estimated gut enzyme activities demonstrated that amylase activity was significantly (P < 0.05) higher in golden mahseer and snow trout compared to hill trout, while total protease, trypsin and chymotrypsin activities were all significantly (P < 0.05) higher in the hill trout compared to other species. A strong co‐relation was found among relative gut length, food composition and digestive enzyme activities of each species. This may guide the future formulation of feed to these important species of carps kept in farm.     

Accumulated snow and summer temperature – critical factors for recruitment to high mountain populations of brown trout (Salmo trutta L.)

Abstract –  In lake Krokavatn, 1236 m a.s.l., only six strong year-classes of brown trout appeared during the period 1970–2003. Eleven year-classes were missing during the same period. The observed recruitment failure depended significantly on the accumulated snow depth in April, whereas the mean August temperature in the year of birth was significant for the appearance of strong year-classes. Size of the young-of-the-year (YOY) trout at onset of the winter seemed to be crucial for survival. Also little snow and low temperatures during the winter may have led to recruitment failure, as small nursery streams may freeze completely under such conditions, as happened during the winter of 1995/1996. Thus, the recruitment to brown trout populations in western high mountain areas of Norway seemed to be strongly affected by accumulated snow depth and summer temperatures. A climate change with more winter precipitation, as predicted for the present century, may therefore be detrimental to recruitment. However, warmer summers may increase recruitment to levels that lead to overpopulation, but also to establishment of brown trout populations at higher elevations than today.     

Movement of adult male snow crab, Chionoecetes opilio, in the southern Gulf of St. Lawrence and eastern Nova Scotia, Canada

A total of 12,755 adult male snow crabs (Chionoecetes opilio) were tagged with spaghetti–Carlin tags in 33 sites throughout the southern Gulf of St. Lawrence (sGSL) and eastern Nova Scotia (eNS) between 1993 and 2003. Of the 1971 tag returns obtained between 1994 and 2004, 1703 had accurate geographical recapture positions. The average distance travelled was 16.7 km for sGSL (maximum 165 km) and 61.5 km for eNS (maximum 368 km). The release site and the number of days at liberty before recapture were significant factors affecting the distance travelled by the crabs. Size had no significant effect on the distance travelled or the direction of movement. The present observations support the sedentary nature previously reported for the sGSL snow crab stock, but not the eNS stock, where the movement of snow crab was more dynamic. In both regions, there were movements between management areas, which indicates that managing the fisheries in discrete units is not warranted.