Climate change could lead to mismatches between the reproductive cycles of marine organisms and their planktonic food. We tested this hypothesis by comparing shrimp (Pandalus borealis) egg hatching times and satellite-derived phytoplankton bloom dynamics throughout the North Atlantic. At large spatial and long temporal (10 years or longer) scales, hatching was correlated with the timing of the spring phytoplankton bloom. Annual egg development and hatching times were determined locally by bottom water temperature. We conclude that different populations of P. borealis have adapted to local temperatures and bloom timing, matching egg hatching to food availability under average conditions. This strategy is vulnerable to interannual oceanographic variability and long-term climatic changes.

Maurice Lamontagne Institute, Fisheries and Oceans Canada, 850 route de la mer, Mont-Joli, Quebec G5H 3Z4, Canada ABSTRACT: Time series of sea-surface temperature (SST), thermally mixed layer depth, and the SST warming rate in spring at the time of larval emergence were correlated with indices of northern shrimp Pandalus borealis recruitment (cohort abundance and larval survival index) between 1994 and 2003 in the northwest Gulf of St. Lawrence, Canada. The recruitment index and larval survival index were negatively correlated to daily mean SST at the time of larval emergence. The recruitment index and larval survival index were positively correlated with the SST warming rate and with the mixed layer depth at the time of larval emergence. Overall, the analysis reveals that larval emergence during a period of weak density stratification and low SST in the spring, but followed by relatively high warming rates of the upper layer of the water column, is favourable for larval survival. We suggest that the observed relationships support the hypothesis that oceanographic conditions in the upper layer of the water column, which initiate and sustain high levels of biological production at the time of larval emergence and early development, are favourable for northern shrimp recruitment success. Thus, interannual variability in northern shrimp recruitment in the northwest Gulf of St. Lawrence may be explained by Cushing's match/mismatch hypothesis.KEY WORDS: Northern shrimp · Sea-surface temperature · Recruitment · Match/mismatch · Gulf of St. Lawrence · Pandalus borealis Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 339: [229][230][231][232][233][234][235][236][237][238][239][240][241] 2007 before the first juveniles descend to the bottom (Ouellet & Allard 2006).In the NW GSL, the first 3 larval stages are present in the water column until early June and are concentrated in the upper layer of the stratified water column, where favourable feeding conditions are expected (Ouellet & Lefaivre 1994, Ouellet & Allard 2006. Gut content and biochemical analyses of field-caught larvae suggest that phytoplankton may constitute a significant proportion of the diet of the first larval stages at sea (Stickney & Perkins 1981, Pedersen & Storm 2002. However, in the laboratory, phytoplankton cells alone cannot support Pandalus borealis larval development and growth (Ouellet et al. 1992). Stage I and II larvae have a higher clearance rate for algal food than for other (animal) food items, but Stage III and older larvae seem to ignore phytoplankton cells (Rasmussen et al. 2000).Investigations carried out in different oceanic regions have suggested that variability in the physical conditions and the spring biological production cycles influences Pandalus borealis abundance and growth (Anderson 2000, Parsons & Colbourne 2000, FuentesYaco et al. 2007). More generally, the notion that variability in larval survival arises from annual variations in the temporal and/or spatial overlap between...

Recent stock assessments for Atlantic Canadian shrimp (Pandalus borealis) stocks, including the Scotian Shelf, the Gulf of St. Lawrence and the Labrador-Newfoundland Shelf, were conducted using the checklist or "Traffic Light" method. Results were viewed positively by many scientists, fisheries managers and industry, and the method has since been adopted by the Northwest Atlantic Fisheries Oganization (NAFO) for "data poor" stocks. It is also being considered by other stock assessment/management organizations. A major drawback of the method in its current form is that it does not link assessments to TACs or other management controls. Modeling results suggest that "Traffic Light" scores can be linked to simple harvest control rules in a way that is consistent with shrimp stock dynamics and management requirements, creating an integrated management framework that could be useful for "data rich" as well as "data poor" stocks.

Ouellet, P., Fuentes-Yaco, C., Savard, L., Platt, T., Sathyendranath, S., Koeller, P., Orr, D., and Siegstad, H. 2011. Ocean surface characteristics influence recruitment variability of populations of northern shrimp (Pandalus borealis) in the Northwest Atlantic. – ICES Journal of Marine Science, 68: 737–744. Remotely sensed data were used to derive simple ecosystem indicators for four regions of the Northwest Atlantic to test the hypothesis that sea surface temperatures (SSTs) and spring phytoplankton bloom characteristics (initiation, timing, intensity, and duration) have a significant influence on larval survival and recruitment of northern shrimp (Pandalus borealis). For all years (1998–2007) and regions, hatching was after the initiation of the bloom and before or after the bloom reached its maximum intensity. The results suggest that the best survival of larvae is associated with high warming rates of SST following hatching, but in very cold environments, warm temperatures at hatching seem to be important for larval survival. The analyses also indicate that larval survival is supported by an early, long phytoplankton bloom which attains high concentrations of chlorophyll a. The results demonstrate the potential of remotely sensed data for deriving simple population-specific ecosystem indicators for potential use in building operational recruitment models for predicting changes in northern shrimp abundance.

Simard, Y., and L. Savard. 1990. Variability, spatial patterns and scales of similarity in size-frequency distributions of the northern shrimp (Pandalus borealis) and its migrations in the Gulf of St. Lawrence. Can. 1. Fish.Aquat. Sci. 47: 794-804.The causes of high variability of length-frequency distributions (LFDs) of the northern shrimp in the Gulf of St. Lawerence were investigated with spatial statistics. The LFD is considered as a multivariate whose spatial structure was analyzed with cluster analysis, dissimilarity variograms and multivariate correlograms. Data were collected in 1984Data were collected in , 1985Data were collected in , and 1987 on the three main shrimp grounds: Sept-lles, North-Anticosti, and Esquiman. The LFDs were spatially autocorrelated over a wide range of scales, and well-defined homogeneous assemblages were observed in each region every year. The autocorrelation signature revealed that the spatial organization resulted from large gradients, partially related to the topography of the shrimp grounds, which probably resulted from the ontogenic depth-migration of the shrimps. The specific mean length of cohorts consistently increased along the spatial gradients, up to about one-half of the annual growth increment. This was attributed to the fact that the migration routes passed through an increasing temperature gradient, which, directly or indirectly, accelerated their growth. Significant regional and interannual differences in the relative proportion of the modal components of LFDs were noted, and were ascribed to fluctuations in the success and distribution of recruitment and survivorship.Les causes de la forte variabilite des distributions de frequence de longueur (DFLs) chez la crevette nordique du Golfe du Saint-Laurent sont etudikes 21 I'aide de statistique spatiales. Les DFLs sont considerees cornme une multivariable dont on 6tudie la structure spatiale au moyen de groupements hikrarchiques, de variogrammes de dissimilarit6 et de corr6logrammes multivariables. Les donnees ont 6t6 recoltees en 1984, 1985, et 1987 dans les trois principales regions de p@che: Sept-lles, Nord-Anticosti, et Esquiman. Les DFLs etaient toujours autocorrelkes suivant un large continuum d'echelles spatiales, et des assemblages homogPnes bien definis ont kt6 observees chaque annee dans chacune des trois regions. La forme d'autocorrelation indiquait que I'organisation spatiale provenait de large gradients, modules par la topographie des regions. Ces gradients resultaient vraisemblablernent de la migration ontogenique des crevettes vers les fonds plus profonds. Les longueur moyennes spkcifiques des cohortes ont montr6 un accroissement systkmatique le long des gradients spatiaux, representant jusqulA la moiti6 de la croissance annuelle. Ceci fut attribue au fait que les routes migratoires croisaient un gradient positif de temp&ature, qui accel&ait, directement ou indirectement, leur croissance. Des differences regionales et interannnuelles considerables de la proportion relative des modes composant les...

Shrimp (Pandalus borealis) length frequency distributions obtained during research surveys in Davis Strait (NAFO Subareas 0+1) from 1983 to 1987 were analyzed for age and growth. Samples were combined within year on the basis of their similarity using cluster analysis. Modal analyses were performed for males only, separating the distribution mixtures into normal components which were interpreted as ages 1 to 6, inclusive. Mean carapace lengths at these ages were estimated at 8.4, 12.3, 15.7, 18.5, 20.6 and 22.7 mm, respectively. Females were separated at ages 7 and 8+ on the basis of biological characteristics with mean lengths of 24.9 and 26.3 mm. A comparison of results from Davis Strait with those reported from other areas in the Northwest Atlantic showed increased longevity and slower growth in the north.

Trawling has been reported worldwide to alter seabed structure, and thus benthic habitats and ecosystems. Usually, a decrease in species richness and biomass is observed, and community structure is modified towards more opportunistic species. The Gulf of St Lawrence (Canada) has been intensely exploited since the 17th century, including net, longline, dredge and trawl fishing activities. Recently, the collapse of groundfish stocks induced a shift in fishing practices toward shrimp trawling, which is currently considered a sustainable fishing activity in the region. However, no long-term study has evaluated the potential effects of trawling disturbances on benthic mega-invertebrates. We investigated whether shrimp trawling had long- (ca. 20 years), mid- (ca. 10 years), and short-term (ca. 4 years) impacts on benthic mega-invertebrate taxa richness, biomass, and community structure. Scientific and fishery trawling data analyses showed that no significant long-, mid-, or short-term effect was detected on taxa richness. Significant but weak effects on biomass and community structure were detected at the mesoscale, i.e. at the scale of fishing grounds. In this long-exploited ecosystem, we suggest that a critical level of disturbance was attained by the first gear passages, which occurred decades ago and had irreversible impacts on the seabed by removing vulnerable taxa and structures that provided three-dimensional habitats. It is likely that benthic communities have subsequently reached a disturbed state of equilibrium on which current trawling disturbance has limited or no further impacts.

A complete linkage cluster analysis using the physical characteristics of the sampling sites has revealed the existence of five groups corresponding to five habitat types nonequally distributed in a northern Quebec river. According to the results of discriminant analysis using the relative abundance of the fish species present, these habitats support populations which differ by the relative abundance of species and not by the presence or absence of some particular species. A habitat is first characterized by a species living preferentially in this habitat, then by the other species inhabiting the area in an opportunistic way, and finally by some satellite species which do not seem to have any marked requirements. A habitat is considered as optimal for a species first if this species inhabits this area preferentially to others and secondly if this use is more advantageous for growth or condition factor. This seems to be confirmed for two of the most abundant species, northern pike (Esox lucius) and lake whitefish (Coregonus clupeaformis), both of which have a higher condition factor and a better growth in the part of the river where their optimal habitat is more frequently found.