Thriving Oceans

It’s an article packed full of potential contention as it speaks to a variety of issues involving fisheries management.  So thank God we are dealing with a charismatic marine species or we just may be contemplating their extinction.  But then again, perhaps we are doing just that since all 7 species of marine turtles are listed under the Endangered Species Act.  So what does that mean when millions of sea  turtles are caught as bycatch in just 18 years?  I think it means the status quo is definitely due for an overhaul to say the least.

Bycatch.  It’s a word that sounds rather innocuous as it rolls off the tongue, but clearly does not do justice to the staggering amount of life that is instantly converted to simple biological waste.  It’s a problem that amounts to tonnes, in the neighborhood of several million per year.  And again I say thank God because the widely popular sea turtle may be able to help shine the light on an ever growing problem responsible for population declines in multiple species.  Well, at least I hope so.

In Global Patterns of Marine Turtle Bycatch, gillnets, longlines, and trawl fisheries are providing us with a perspective that we would probably rather ignore.  Unfortunately the out of sight out of mind attitude is not helping the sea turtle situation and it reminds me of an old mantra I used, “The catch of the day may cost more than you think.”  In this scenario, that cost is…

The total reported global marine turtle bycatch (1990-2008) was ∼85,000 turtles, but due to the small percentage of fishing effort observed and reported (typically <1% of total fleets), and to a global lack of bycatch information from small-scale fisheries, this likely underestimates the true total by at least two orders of magnitude.

And after looking at the data I am left wondering how many sea turtles are actually killed or die as a result of wounds incurred by coming into contact with gillnets, longlines and trawls.  I can imagine it is only palatable when wearing a pair of rose colored glasses.  But as far as the research goes, there was insufficient data to incorporate mortality rates.

The study found the bycatch per unit effort (BPUE) varied greatly depending upon the region and fishing method employed.  In fact , it identified certain hotspots that are a cause for concern and highlight the need for fisheries management intervention.

Based on reported sea turtle bycatch, the maximum BPUEs found for each fishing method are as follows:

• 2.2 turtles per set for gillnets in the Mediterranean Sea
• 19.3 turtles per 1,000 hooks for longlines in the eastern Pacific Ocean
• 7.2 turtles per haul for trawls in the southwest Atlantic Ocean

“Targeted action to reduce turtle-gear interactions is essential for population persistence, and is already underway for some fleets…our study revealed that reports of longline bycatch are two-fold more common than reports of bycatch in either trawls or gillnets.”

Having the data means we have no more excuses for not developing, continuing to develop and implementing a conservation plan that is both regional and fishing gear specific.  The plan must be more than focusing on turtle excluder devices, but must include other innovative management techniques on the lines of time-area closures, etc.  And since time is of the essence and marine turtle populations are at risk, immediate action is required.

Wallace, B., Lewison, R., McDonald, S., McDonald, R., Kot, C., Kelez, S., Bjorkland, R., Finkbeiner, E., Helmbrecht, S., & Crowder, L. (2010). Global patterns of marine turtle bycatch Conservation Letters DOI: 10.1111/j.1755-263X.2010.00105.x

A new publication in Conservation Biology is shedding light on the effect of a low population on fertility success in sea turtles.  And unlike other species that experience reduced fertility when population densities drop, green sea turtles, loggerhead sea turtles, and their conservationists are receiving a bit of good news. 

“We found that there has been no reduction in fertility in small nesting aggregations in either of these species worldwide.”

The well known issue of sea turtle overexploitation has sparked recovery efforts around the globe.  But the lingering question was whether some turtle populations have passed the point of no return and would thus be unable to ultimately avoid extinction.  According to researchers, marine species have had a variable success rate in recuperating from low numbers, which is a product of the biology of the species and human pressures like habitat degradation and harvesting.  However, these latest findings suggest that even populations comprised of very low densities have a chance at recovery (Previous critical density models indicated depensation might occur when populations dipped below 5% of historical numbers).

“Furthermore, there was clearly no pronounced reduction in fertility in either species at low numbers, even in rookeries yielding as few as 10 clutches per year.”

 

“The capacity to maintain functional levels of fertilization success in the face of high levels of exploitation may help in part to explain why total extirpations have been few and recoveries have been possible.  This information does not, however, explain why in some cases recovery has not occurred.”

I guess the biological moral of the story is that even highly reduced populations have an “intrinsic conservation value”, and can provide much needed information in sea turtle biology and aid in global recovery efforts.

BELL, C., BLUMENTHAL, J., BRODERICK, A., & GODLEY, B. (2009). Investigating Potential for Depensation in Marine Turtles: How Low Can You Go? Conservation Biology DOI: 10.1111/j.1523-1739.2009.01313.x

TODAY IS A GREAT DAY FOR SEA TURTLES!  Check out the following press release:

NASSAU, Bahamas — The Ministry of Agriculture and Marine Resources hereby announces that the Fisheries Regulations governing marine turtles have been amended to give full protection to all marine turtles found in Bahamian waters by prohibiting the harvesting, possession, purchase and sale of turtles, their parts and eggs. The new regulations also prohibits the molestation of marine turtle nests.

The regulations will come into effect on Tuesday, September 1st, 2009.

The Government has engaged in intensive and extensive consultations with the public over the issue of the ban on the harvesting and sale of marine turtles for the past twelve months. The commitment to the conservation and preservation of these species while in Bahamian waters has been demonstrated by the introduction of protective measures and safeguards over the past two decades, starting with the actions taken to safeguard the hawksbill turtle in 1986.