Geopositioning underwater acoustic telemetry was used to test whether rapid recompression with weighted return-to-depth (descender) devices reduced discard mortality of red snapper (n = 141) and gray triggerfish (n = 26) captured and released at 30–60 m depths at two 15 km2 study sites in the northern Gulf of Mexico. Cox proportional hazards modelling indicated red snapper released with descender devices had significantly lower discard mortality within the first 2 d (95% CI = 18.8–41.8% for descender-released vs. 44.0–72.4% for surface-released, unvented fish), while there was no significant effect of descender devices on discard mortality of gray triggerfish. Predation by large pelagic predators was estimated to account 83% of red snapper and 100% of gray triggerfish discard mortality. Discard mortality due to predation has likely been overlooked in previous mark-recapture, laboratory, and enclosure studies, suggesting cryptic population losses due to predation on discards may be underestimated for red snapper and gray triggerfish. Large-area three-dimensional positioning acoustic telemetry arrays combined with collaboration and data sharing among acoustic telemetry researchers have the potential to advance our knowledge of the processes affecting discard mortality in reef fishes and other taxa.

Marine ecosystems are dynamic, often have open boundaries, and their overall productivity responds nonlinearly to multiple drivers acting at multiple temporal and spatial scales, under a triad of influences: climatic, anthropogenic, and ecological. In order to further our understanding of how the structure and functioning of marine ecosystems influence and regulate patterns of fisheries production, and how they are affected by this triad of drivers, a comparative approach is required. We apply a system-level surplus production modeling approach to the total aggregated catch and biomass of all major targeted fish species in 12 exploited Northern Hemisphere ecosystems. We use 2 variations of a surplus production model: a regression model and a dynamic model, each fit with and without environmental and biological covariates. Our aims were to explore (1) the effects of common drivers at the basin scale and their relative influence within the triad of drivers among systems, (2) the impact of covariates on biological reference points and implications for fisheries management, and (3) the relationship between maximum sustainable yield (MSY) and production. Our results show that the environment affects estimates of systemlevel MSY across all ecosystems studied and that specifically water temperature is a major influence on productivity. Emergent properties of northern hemisphere systems suggest that MSY values and optimal exploitation rates are relatively consistent: MSY ranges between 1 and 5 t km . Finally, we suggest that the relationship between fisheries yield and primary production is not as simple as suggested in other studies. These results put fisheries in a broader ecosystem context and have implications for an ecosystem approach to management.

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