New study takes a big step in solving the seemingly relentless battle between fisheries and conservation biologists
Research study review written by: Jenny Groover
Fisheries and conservation biologists are known for being wrought in conflicting interests. While fisheries seek to maximize their financial gain through large catches they can export, conservation biologists seek to preserve aquatic habitat sustainability and prevent extinction. A new study published August 2012 in Fisheries Research titled “The reproductive cycle of Octopus cyanea in southwest Madagascar and implications for fisheries management” seeks to remedy this seemingly interminable quarrel.
The sponsoring organization of this research study, Blue Ventures, is a social enterprise that conducts research and works with local communities of marine and coastal environments to protect biodiversity while helping relieve poverty. Author Daniel Raberinary, community conservation coordinator for Blue Ventures who holds masters and DEA degrees in applied oceanography from the University of Toliara’s IHSM, and Sophie Benbow, Southwest regional coordinator for Blue Ventures who holds an honors degree in Zoology from Durham University and a masters in conservation at University College London, worked together to assess octopus stock collected by Madagascar fishers. The results from their study, which examined octopi reproductive stages, show that supporting fishing closures during June and August or September and October would allow for more octopi to reach sexual maturity. The octopi’s larger weight will bring the fisheries more money and reaching sexual maturity before being fished will insure population sustainability.
Fishing of Octopus cyanea across thirty kilometers of coastline along the Mozambique Channel on the southwest coast of Madagascar was assessed from February 2005 to February 2006. Octopus weight, weight and length of extracted gonads, octopus sex, in-field visual assessment of gonad maturity, total length, mantle length, diameter and arrangement of spermatophores or maximum diameter and length of oocytes were measured. Results showed that less than one percent of the females caught were at sexual maturity whereas almost seventy percent of males were. Further, by calculating when peak spawning occurred and observing the effects of a fishing ban in January 2006, the researchers found a recruitment peak during August and September that supports the hypothesis that avoidance of fishing during that time would allow larger, more sexually mature adults the following month.
The researchers pointed out that although placing fishing bans during peak recruitment times would be beneficial, this is only true given the current fishing practices. Most octopi fisheries of Madagascar fish along the reef tables. Sexually mature females are known to dive deeper to avoid predation, which explains why the numbers collected of fished sexually mature females were so low. New methods of fishing using traps rather than spear-fishing, which damages the mantle, have become increasingly popular, allowing the fishing of sexually mature female octopi even at cavernous depths. The Octopus cyanea fishery is the most prosperous fishery in southwest Madagascar and thus plays a crucial economic role. The results of this study substantiate the need for fishery management to address seasonal bans and permitted methodology to minimize harm to Octopus cyanea populations while still maximizing fisher gains. Allowing octopi to reach sexual maturity will result in an increased weight that maximized fisher profit while also insuring enough reproduction for population stability.
One of the challenges these scientists faced in determining the reproductive cycle of Octopus cyanea was discerning weight correlations with sexual maturity. Males showed a much higher correlation between weight and sexual maturity than females. Female maturity designation was more consistent with oocyte diameter. The authors held a goal of establishing concrete methodology of measuring octopi maturity so that local fishery management could continue to monitor population health. Rather than working against fisheries by trying to shut them down for long periods of time, Raberinary and Benbow advocate looking closely at reproduction cycles and then working with fisheries. These researchers set a precedent for future studies of species’ reproductive cycles to determine best practices that benefit conversationalists and fishers at the same time.
D. Raberinary, S. Benbow, The reproductive cycle of Octopus cyanea in southwest Madagascar and implications for fisheries management, Fisheries Research, Volumes 125–126, August 2012, Pages 190-197, ISSN 0165-7836, 10.1016/j.fishres.2012.02.025.