Bycatch interactions with deep-sea elasmobranchs are increasingly common and can lead to dramatic declines in abundance over short time scales. Sharks hooked in the deep sea could face a higher likelihood of severe physiological disturbance, at-vessel mortality, and post-release mortality (PRM) than their shallower counterparts. Unfortunately, robust PRM rates have not yet been estimated for longline-caught deep-sea sharks, and as such are not currently incorporated into total fishery mortality estimates or bycatch assessments, limiting the effectiveness of current conservation or management initiatives. We empirically estimated PRM for 2 focal taxa of deep-sea shark, the Cuban dogfish Squalus cubensis and the gulper shark Centrophorus sp., using post-release enclosures deployed at-depth. We calculated 24 h PRM rates of 49.7 ± 8.5% (mean ± SE) for S. cubensis and 83 ± 16% for Centrophorus sp. and identified blood lactate, total length, glucose, and vitality scores as predictors of PRM in S. cubensis. We also observed all 24 h PRM within 11 h post-capture and demonstrated the effects of recovery depth and at-vessel blood chemistry metrics on post-release behavior. Our results suggest that PRM rates of deep-sea sharks are high and highlight the need for filling in this gap in fishery mortality estimates for other common discards in the future.

Experiments were conducted aboard longline vessels operating in the Seychelles targeting swordfish and tuna. Experimental longlines fitted with hook timers and temperature depth recorders were used to identify differences in species composition, quantity and depth of catch between night sets using a shallow basket (swordfish target) and day sets using both shallow and deep baskets (tuna target). The majority of species were caught during day sets (75%). Lancetfish was the main bycatch species during daytime sets. Sharks were the most common nightime bycatch species, with blue and shortfin mako sharks being the predominant shark species. All marketable species were caught in the 150 m layer, marlins were never caught below 100 m. Sharks were caught below 150 m during both night and day sets. For other bycatch species, all were caught in depths less than 150 m during night sets. Daytime depth captures varied.

Trials were conducted using excluder grids on trawls targeting Norway lobster (Nephrops novegicus) and greater forkbeard (Phycis blennoides) in the Tyrrhenian Sea. The excluder grids were tested for their ability to reduce the incidental capture of blackmouth catshark (Galeus melastomus).  In order to estimate the number of escaped fish, covers were placed over the escape outlet before the grid and over the codend. The 90 mm excluder grid did not result in reduced catches of blacknouth catshark. The grid did result in decreased catches of greater forkbeard and Norway lobster, to a smaller degree. Explorative simulations suggest a smaller grid spacing of 70 mm may prove more effective at reducing blackmouth catsharks catches.

An excluder grate (grid) was tested in the silver hake trawl fishery in Massachusetts Bay to determine it's effectiveness in reducing spiny dogfish bycatch.  The effects of color (white or black), angle and direction of the 50 mm spaced grids were investigated through video observations and data collection.  The number of spiny dogfish caught in trawls with the excluder grate were greatly reduced for all gear configurations, while the number of target species caught remained within typical commercial quantities.  Over 88% of spiny dogfish were excluded by the grate regardless of color or gear configuration.  There were no observed differences in the behavior of spiny dogfish between gear configurations or grate colors.