Cephalopods have become an important global food source, but their sustainable management is challenged by unique life history characteristics associated with short lifespans and semelparous reproduction, high natural mortality rates, rapid and often nonasymptotic growth, and complex population structures. Weak stock-recruitment relationships together with the time-consuming work required for age validation and high-volume annual age determinations make traditional age-based modelling impractical. We propose that the best method for cephalopod assessment involves innovative depletion models, fitted with in-season data on catch numbers and fishing effort, to produce realistic estimates of stock biomass. A “fast lane” assessment approach is suggested that includes high-frequency data collection for separate, in-season stock assessments of each cohort to ensure sustainable exploitation of these short-lived resources. However, most cephalopod fisheries are data-poor and/or lack the infrastructure and resources needed to apply depletion methods; therefore, we also present alternative assessment methods that have been recently applied worldwide. We also offer suggestions for further research on the remaining challenges of cephalopod stock assessment and management.

of bio-acoustic surveys near the Pribilof Islands, Alaska, (AK), from which age-0 walleye pollock school and zooplankton patch locations have been extracted, were analysed using image-processing methods. Multiple passes along four transects in this major pollock nursery area were examined. The data showed high year-to-year variability in overall abundance of both fish and plankton, but consistent abundance differences between the transects. Juvenile pollock abundance was generally highest in the shallow shelf region to the north of the Pribilof Islands and lowest in the mouth of the Pribilof Canyon to the south. Plankton biomass patterns tended to be the reverse. We identified fronts and regions within the transects based on changes in hydrograpy (e.g. vertical stratification) and bathymetry. Diel migration patterns of pollock and zooplankton within these regions appear to depend on the degree of stratification, the depth, the size of the pollock and the relative abundance of the pollock and zooplankton. Several hypotheses are also discussed concerning the relationship of pollock recruitment year-class strength to large year classes including differences in the environmental conditions, the pervasiveness of the pollock, the size of juvenile pollock and the density of predators.

The eastern Patagonian Shelf and continental slope of the south-west Atlantic Ocean support a high biodiversity and abundance of skates. In this study, meso-scale differences in the assemblages, spatial and seasonal distributions of skates are revealed among six habitat zones of the eastern Patagonian Shelf characterized by distinctive oceanographic conditions. Most skates belonged to temperate fauna, and their abundance was much greater in habitats occupied by temperate waters (north-western outer shelf) or mixed waters (northern slope) than in habitats occupied by sub-Antarctic waters (SASW) (south-eastern outer shelf and southern slope). Sub-Antarctic skates were not abundant on the shelf even in habitats occupied by SASW, occurring mainly in deep areas of the lower continental slope. The majority of temperate skates migrated seasonally, shifting northward in winter and spreading southward with warming waters in summer. Most temperate species had two peaks in female maturity (mainly spring and autumn) and spawned in the same habitats where they fed. It is hypothesized that the high biodiversity and abundance of skates on the Patagonian Shelf and Slope are due to the practical absence of their natural competitors, flatfishes, which occupy similar eco-niches elsewhere.

Hexagenia nymphs are sensitive to hypoxia, and their abundance has been proposed as an ecosystem indicator for assessing the recovery from eutrophication of shallow, mesotrophic lakes. Acute oxygen tolerance limits are known for Hexagenia spp., but effects of prolonged exposure to sublethal levels of hypoxia are not. A series of 21-day laboratory experiments was conducted to determine the influence of hypoxic stress (range 2-12.6 mg/L dissolved oxygen) and temperature (range 4-20°C) on survival and growth of Hexagenia limbata nymphs. Oxygen and temperature together explained 89% of the variability in survival among H. limbata, and 71% of the variability in average growth. Survival increased with increasing oxygen concentration, reaching an asymptote at 7-8 mg/L. Survival increased with temperature to an asymptote at approximately 9.5°C. Higher temperatures magnified the effects of hypoxia on survival. Growth increased with both oxygen and temperature, and did not reach an asymptote at levels up to 12.6 mg/L oxygen and 20°C. Persistent, sublethal oxygen stress (concentrations <7 mg/L) and reduced temperature (<20°C) can influence both survival and size of H. limbata. Résumé : Les nymphes d'Hexagenia sont sensibles à l'hypoxie, et on a proposé d'utiliser leur abondance comme indicateur écosystémique pour évaluer le rétablissement après eutrophisation des lacs mésotrophes peu profonds. On connaît les limites de la tolérance à une concentration aiguë d'oxygène chez Hexagenia, mais pas les effets d'une exposition prolongée à des niveaux sublétaux d'hypoxie. Nous avons mené une série d'expériences de 21 jours en laboratoire pour déterminer l'influence du stress hypoxique (fourchette 2-12,6 mg/L d'oxygène dissous) et de la température (fourchette 4-20°C) sur la survie et la croissance des nymphes d'Hexagenia limbata. Combinés, l'oxygène et la température expliquaient 89% de la variabilité de la survie parmi les H. limbata et 71% de la variabilité de la croissance moyenne. La survie augmentait avec la concentration d'oxygène, pour atteindre une asymptote à 7-8 mg/L. La survie augmentait en fonction de la température pour atteindre une asymptote à environ 9,5°C. La hausse des températures amplifiait les effets de l'hypoxie sur la survie. La croissance augmentait en fonction à la fois de l'oxygène et de la température, et n'avait pas atteint une asymptote à des niveaux de 12,6 mg/L d'oxygène et 20°C. Un stress persistant et sublétal dû à la concentration de l'oxygène (<7 mg/L) et une réduction de la température (<20°C) peuvent avoir un effet sur la survie et sur la taille d'H. limbata.

Seasonal changes in relative abundance and biomass of nektonic predators were analysed on the eastern Patagonian Shelf and continental slope; one of the most productive large marine ecosystems of the southern hemisphere. Several migratory types were revealed for species belonging to either temperate or sub‐Antarctic faunas. Despite high productivity, only a few large nektonic predators spend their entire life cycle on the eastern Patagonian Shelf and use only a small proportion of the meso‐nektonic resource. Most of the resource is exploited by non‐resident nektonic migrants, which move to the area from distant spawning grounds. Pelagic and demersal sharks and skates, the squid Illex argentinus, tunas and gadoids migrate to the eastern part of the Patagonian Shelf to feed at different times of the year; arriving in seasonal waves according to their life cycle and spawning seasonality. Some deepwater fishes and squid migrate onto the shelf as juveniles to harvest the resource, and then return to deepwater habitat as adults. It is hypothesized that the large biomass of meso‐planktonic and meso‐nektonic consumers prevents most higher‐trophic level predators from establishing spawning populations in this area, as their larvae and fry would be overwhelmed by predation. Instead, the higher‐trophic level predators establish spawning and nursery grounds elsewhere and arrive to feed on the meso‐planktonic and meso‐nektonic resources after they have outgrown their own stages of predation vulnerability.