Long-Term Effectiveness, Failure Rates, and “Dinner Bell” Properties of Acoustic Pingers in a Gillnet Fishery

Abstract

The long-term effectiveness of acoustic pingers in reducing marine mammal bycatch was assessed for the swordfish and thresher shark drift gillnet fishery in California. Between 1990 and 2009, data on fishing gear, environmental variables, and bycatch were recorded for over 8,000 fishing sets by at-sea fishery observers, including over 4,000 sets outfitted with acoustic pingers between 1996 and 2009. Bycatch rates of cetaceans in sets with ≥30 pingers were nearly 50% lower compared to sets without pingers (p = 1.2 × 10−6), though this result is driven largely by common dolphin (Delphinus delphis) bycatch. Beaked whales have not been observed entangled in this fishery since 1995, the last full year of fishing without acoustic pingers. Pinger failure (≥1 nonfunctioning pingers in a net) was noted in 3.7% of observed sets. In sets where the number of failed pingers was recorded, approximately 18% of deployed pingers had failed. Cetacean bycatch rates were 10 times higher in sets where ≥1 pingers failed versus sets without pinger failure (p = 0.002), though sample sizes for sets with pinger failure were small. No evidence of habituation to pingers by cetaceans was apparent over a 14-year period of use. Bycatch rates of California sea lions in sets with ≥30 pingers were nearly double that of sets without pingers, which prompted us to examine the potential “dinner bell” effects of pingers. Depredation of swordfish catch by California sea lions was not linked to pinger use—the best predictors of depredation were total swordfish catch, month fished, area fished, and nighttime use of deck lights on vessels.

To ping or not to ping: the use of active acoustic devices in mitigating interactions between small cetaceans and gillnet fisheries

“…In neither case is there evidence of a long-term increase in bycatch rates (as would reflect a diminution in their efficacy) when the recommended numbers of functioning pingers are used on each string of nets (Palka et al 2008, Carretta & Barlow 2011.…”

“…Since the implementation of pingers in this fishery, the entanglement rate of common dolphins has been reduced by approximately half (Carretta & Barlow 2011), and bycatch of beaked whales has been eliminated (Carretta et al 2008). Comparison of recent bycatch rates with those observed soon after adoption of pingers shows no evidence of habituation.…”

“…Hence, in this fishery, like that in the Gulf of Maine, pingers have been effective in reducing cetacean bycatch, though not to the level seen in the preceding controlled experiments. Pinger failure is an important issue in this fishery too; sets with 1 or more failed pingers had a significantly higher bycatch rate of cetaceans than sets that were fully equipped with functional pingers (Carretta & Barlow 2011).…”

“…On observed vessels, compliance with the requirement to use pingers has remained > 98% since they were made mandatory (Carretta & Barlow 2011). An increasing fraction of the vessels in the CaliforniaOregon fishery (11 of 34 in 2009) are regarded as being too small to accommodate observers, so compliance and bycatch in this part of the fleet is unknown.…”

Technical Measures in Order to Decrease Interactions Between Dolphins and Fishermen: Pingers

“…It is significantly important to carry out researches to investigate that if dinner bell effect which occurs especially with pinnipeds is a real threat for dolphins or not (Franse, 2005). In a long term study conducted by Carretta and Barlow (2011) between 1990, although habituation was not apparent in the in the drift gillnet fishery for swordfish and thresher shark in California, it was outlined that depredation of swordfish catch by California sea lions and bycatch of those animals increased over time with pinger usage pointing the "dinner bell effect". However authors argued that continuing increase in California sea lion numbers were more likely responsible rather than pinger usage.…”