Sea Turtle Bycatch Mitigation in U.S. Longline Fisheries

Abstract

Capture of sea turtles in longline fisheries has been implicated in population declines of loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea) turtles. Since 2004, United States (U.S.) longline vessels targeting swordfish and tunas in the Pacific and regions in the Atlantic Ocean have operated under extensive fisheries regulations to reduce the capture and mortality of endangered and threatened sea turtles. We analyzed 20 + years of longline observer data from both ocean basins during periods before and after the regulations to assess the effectiveness of the regulations. Using generalized additive mixed models (GAMMs), we investigated relationships between the probability of expected turtle interactions and operational components such as fishing location, hook type, bait type, sea surface temperature, and use of light sticks. GAMMs identified a two to three-fold lower probability of expected capture of loggerhead and leatherback turtle bycatch in the Atlantic and Pacific when circle hooks are used (vs. J hook). Use of fish bait (vs. squid) was also found to significantly reduce the capture probability of loggerheads in both ocean basins, and for leatherbacks in the Atlantic only. Capture probabilities are lowest when using a combination of circle hook and fish bait. Influences of light sticks, hook depth, geographic location, and sea surface temperature are discussed specific to species and regions. Results confirmed that in two U.S.-managed longline fisheries, rates of sea turtle bycatch significantly declined after the regulations. In the Atlantic (all regions), rates declined by 40 and 61% for leatherback and loggerhead turtles, respectively, after the regulations. Within the NED area alone, where additional restrictions include a large circle hook (18/0) and limited use of squid bait, rates declined by 64 and 55% for leatherback and loggerhead turtles, respectively. Gains were even more pronounced for the Pacific shallow set fishery, where mean bycatch rates declined by 84 and 95%, for leatherback and loggerhead turtles, respectively, for the post-regulation period. Similar management approaches could be used within regional fisheries management organizations to reduce capture of sea turtles and to promote sustainable fisheries on a global scale.

Feeding behavior and visual field differences in loggerhead and leatherback sea turtles may explain differences in longline fisheries interactions

“…Several approaches are used to reduce sea turtle bycatch in fisheries worldwide (Kerstetter & Watson 2006, Gilman & Huang 2017, Swimmer et al 2017. A common approach is to change the bait and hook type to decrease bycatch, although some time-area fisheries closures are also implemented.…”

“…Several advances have been made to reduce sea turtle bycatch, such as time fished, bait type used, hook type (circle vs. J-hooks) and barb offset, and bait soak times (Shiode et al 2005, Watson et al 2005, Gilman et al 2006, Lucchetti & Sala 2010, Santos et al 2012, Stokes et al 2012, Swimmer at al. 2017).…”

“…These efforts include changing the bait types to decrease the likelihood of interactions with sea turtles. Several studies found that the bycatch of sea turtles decreased significantly with the use of fish bait rather than squid (Foster et al 2012, Santos et al 2012, Swimmer et al 2017. Altering the type of hook is another technique to reduce bycatch.…”

“…Most bycaught loggerheads tend to be hooked in the mouth or internally in the throat, stomach, or intestines (Gilman et al 2006). In contrast, most bycaught leatherbacks are foul-hooked or entangled in the gear (Epperly et al 2012, Swimmer et al 2017.…”

Conservation implications of sea turtle nesting trends: elusive recovery of a globally important loggerhead population

“…, Gilman and Huang , Swimmer et al. ), the issue of bycatch is far from being resolved and continues to pose a serious threat to sea turtle recovery (Wallace et al. , Rees et al.…”