Sarasota dolphins serve as model for evaluating fates of dolphins injured in fisheries
By Randall Wells, PhD

Figure 1. Sarasota Bay bottlenose dolphin "FB 100" upon necropsy by Mote's Stranding Investigations Program, showing the large single hook and the treble hooks of a fishing lure embedded in the throat and "goosebeak." Such injuries eventually result in death.

      NOAA’s Fisheries Service (NMFS) is charged under the federal Marine Mammal Protection Act (MMPA) with responsibility for reducing deaths and serious injuries of marine mammals from fisheries.   NMFS is tasked with determining whether injuries from entanglement in, or ingestion of, commercial fishing gear, or other interactions with humans are likely to lead to mortality.  The determinations of numbers of mortalities lead to decisions about whether, for example, fisheries are allowed to continue or must modify their activities to come into compliance with the MMPA.  When a dolphin is last seen swimming with gear attached to it, for example, as occurs with pilot whales or Risso’s dolphins in pelagic longline fisheries, or with a major laceration from a vessel strike, it is difficult to evaluate the seriousness of the injury and predict whether the animal will survive.  As an alternative to offshore studies, it has been possible to obtain relevant data under more tractable circumstances, from our long-term data on the bottlenose dolphins of Sarasota Bay, Florida
       In September, I presented an invited paper on the consequences of serious injuries on dolphin survival and reproduction at the NOAA/NMFS Serious Injury Technical Workshop in Seattle.  Our long-term research was acknowledged as being the best source of data available on this issue for small cetaceans.  We are preparing a publishable manuscript based on the presentation, as defensible, peer-reviewed findings are needed by NMFS in making decisions that are likely to lead to law suits by the commercial fishing industry.
      Several kinds of injuries seem to have a high probability of leading to mortality, including ingestion of fishing gear when it involved hooks becoming embedded in the throat, the goosebeak, or the esophagus, and line wrapped around the goosebeak.  Multiple, constrictive wraps of line around the body, and especially at the insertions of the fins, lead to deep lacerations that can result in amputation, blood loss, impaired mobility, or infection.  Although dolphins with ingested gear and severe entanglements were often still able to swim following their initial encounter with the gear, mortality was likely to have occurred eventually.  A reasonable precautionary approach would be to consider dolphins with ingested gear or severe constrictive entanglements around the flipper and fluke insertions as mortalities.

Figure 2. Flipper of bottlenose dolphin "Toro" showing the lesions resulting from multiple constrictive wraps of line.

      Other severe injuries are less likely to lead to death.  Vessel strike injuries from propellers appeared to be survivable if they involved only soft tissue, and not bones.  Dolphins have been observed to survive amputations or disfigurements of the distal ends of flippers, flukes, and dorsal fins from lines and undetermined causes.  It is important to note, however, that evaluations of healed wounds do not take into account the possibility of immediate mortalities from similar injuries. 
      Extrapolations of findings and conclusions from injured coastal bottlenose dolphins to other cetacean species facing similar issues but with different gear or vessels must be done with caution and with consideration of the best information available from the specific situation of concern.  However, in the absence of adequate information for specific species or fisheries, the bottlenose dolphins of Sarasota Bay can serve as a useful surrogate for modeling impacts.  NOAA’s Fisheries Service will be using a write-up of this presentation as a background document for its joint meeting of the Atlantic, Pacific, and Alaskan Scientific Review Groups in January 2008 in Monterey, California.