We hear so much bad news about sharks – populations of many species have declined to historic lows, finning occurs in numerous countries, bycatch continues to threaten shark species, shark fishing tournaments are conducted for sport here in the US. When a bit of good news about sharks comes along it seems natural to be encouraged that perhaps the situation is turning around. Yet I hesitated to write up the article that follows – would any bit of good news about shark recovery be used to encourage continued hunting, to justify reduced adherence to existing protections, or the failure to enact new ones? Many people work tirelessly in shark conservation, however, and they deserve to take pride in some encouraging news…..while acknowledging there is still a long way to go.
One technique researchers often use to address large-scale questions, whether assessing environmental conditions or determining the effectiveness of a cancer drug, is called meta-analysis. Basically this technique combines individual small studies so their data can be used to draw more robust conclusions. While these meta-analyses must be rigorously controlled, and there are many variables that must be addressed, when done successfully a meta-analysis can be far more powerful than its individual components.
Peterson et al performed an ecological meta-analysis to investigate the current status of US coastal shark populations. They combined data from six different surveys along the US Atlantic and Gulf coasts, assessing numbers of small and large coastal shark species.
Among the large coastal shark species surveyed – sandbar, spinner, tiger and blacktip sharks – declines of 60-99% over historical numbers had been seen into the 1990s. For all of these species, the current study found that significant increases over the lowest levels had occurred since the implementation of the Shark Fishery Management Plan (FMP) by NOAA in 1993. As might be expected, increases were greater for those sharks that reproduce at a younger age and/or have a greater number of pups, than for late-reproducing species or those who have fewer offspring.
The smaller shark species evaluated – Atlantic sharpnose, bonnethead, Atlantic blacknose and Gulf of Mexico blacknose – had experienced declines that were somewhat less dramatic than for the larger sharks, between 35 and 80%, probably a result of their faster reproduction times. These small sharks have a more limited range and reduced migration relative to the larger sharks, however, and so the authors found more variability in their overall recovery. Increases were seen for Atlantic sharpnose, bonnethead, and Atlantic blacknose, but not for Gulf of Mexico blacknose. Gulf of Mexico blacknose sharks may still be reduced due to significant bycatch in shrimp fisheries.
Overall, the authors make a case for “preliminary recovery” of several species of shark along the southeastern US Atlantic coast. There is a great deal more information in the paper, for example the effects of yearly changes in temperature, rainfall and current strength on shark numbers. Given rapid declines in recent past history, even small increases in numbers are good news for sharks!
The article is: Peterson, CD, Belcher, CN, Bethea, DM, Driggers, WB, Frazier, BS and Latour, RJ. Preliminary recovery of coastal sharks in the south-east United States. (2017) Fish & Fisheries, DOI: 10.1111/faf.12210.