Blue sharks Prionace glauca are the most frequently discarded fish species during commercial pelagic longline fishing operations worldwide, yet their post-release mortality rate has never been measured. A generalized linear model of 12 404 blue sharks observed during the Canadian Atlantic pelagic longline swordfishery suggested a hooking mortality of 12 to 13%, yet scientific examination of 902 of these sharks indicated that hooking mortality was actually higher. A random sample of 40 of these blue sharks were tagged with satellite pop-up archival transmission (PAT) tags, then monitored for periods of up to 6 mo after release. All of the surviving sharks exhibited a depthholding recovery behaviour for a period of 2 to 7 d after release. All healthy sharks survived, while 33% of those that were badly injured or gut hooked subsequently died. Overall blue shark bycatch mortality in the pelagic longline fishery was estimated at 35%, while the estimated discard mortality for sharks that were released alive was 19%. Survival time models indicated that 95% of the mortality occurred within 11 d of release, indicative of death by trauma rather than starvation. The annual blue shark catch in the North Atlantic was estimated at about 84 000 t, of which 57 000 t is discarded. A preliminary estimate of 20 000 t of annual dead discards for North Atlantic blue sharks is similar to that of the reported nominal catch, and could substantially change the perception of population health if incorporated into a population-level stock assessment. KEY WORDS: Discard mortality · Hooking mortality · Tagging · Bycatch · Satellite tags Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 387: [241][242][243][244][245][246][247][248][249][250][251][252][253] 2009 ronmental conditions at the time of release (Davis 2002). The difficulty in quantifying post-release mortality is due to the scarcity and/or expense of methods for tracking released fish in the wild over periods of time of up to several months. Most studies have attempted to avoid this issue by holding fish in cages or pens for several days after capture (e.g. Neilson et al. 1989). However, holding pens provide a clearly artificial and spatially constrained environment, and thus have the potential to introduce (or avoid) sources of mortality that would not be present under natural, free-swimming conditions. As a result, some sort of tag-recapture or telemetry program is required to properly estimate the post-release mortality rate of discarded fish (Davis 2002, Pollock & Pine 2007, Skomal 2007. Such a program would be well suited for monitoring released fish in the wild for extended periods of time, and has been successfully applied in estimating short-term discard mortality rates in large pelagic fish such as striped marlin (Tetrapturus audax) (Domeier et al. 2003). An additional advantage of such studies is that evidence of physical trauma or stress indicators from blood chemistry can ultimately be linked to the subsequent s...

Recent advances in our understanding of the spatial behavior of white sharks have been based on only 3 geographical areas: the waters off Australia, southern Africa, and the northeast Pacific Ocean. Here we report results from the first study in New Zealand waters using satellite tags to study sharks. We attached pop-up archival tags to 4 white sharks Carcharodon carcharias at the Chatham Islands, New Zealand, during April 2005. One tag released prematurely, but 3 others showed long-distance northward movements of 1000 to 3000 km across the open ocean, with 2 sharks moving to the tropical islands of New Caledonia and Vanuatu. Our results are similar to recent findings elsewhere of fast oceanic travel and well oriented navigation. Circumstantial information suggests that some of these movements could be part of a regular foraging migration where white sharks visit humpback whale wintering grounds to feed on carcasses and prey on newborn calves. Before embarking on large-scale movements, all sharks remained over the continental shelf near the Chatham Islands for 2.6 to 5.0 mo, rarely swimming deeper than 100 m. In contrast, during oceanic large-scale movements, they spent most of their time in the top 1 m of water, showing periodic dives to depths over 900 m. The diving behavior in combination with the large-scale movements from temperate to tropical waters results in the sharks experiencing a very wide range of water temperatures.

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Twenty-three-gauge pars plana vitrectomy demonstrates short-term visual outcomes and complication rates that are comparable to those reported with 20- and 25-gauge systems.