I am currently conducting research on a flying fish roe fishery in Taiwan. This is a very unique fishery as it targets the egg instead of the adult fish (i.e., essentially, no fishery for the adults). Fishers collected eggs using straw mats deployed on the sea surface. We can calculate CPUE based on the catch (in terms of weight) and effort (in terms of vessel number, or no. of straw mat deployed) data of the fishery. After several years of data collection, we can now understand the resource trend based on a standardized CPUE series calculated from fishery operations (such as vessel size, targeting vs. non-targeting, etc.) and environmental data (such as SST, rainfall, etc.). However, we also wish to know the possible sustainable yield of the fishery. Thus, we tried to use the CPUE and the data to estimate the MSY for the fishery, but such an approach may violate assumptions of the model as “egg” does not grow, and have a surplus production. An alternative way is to convert eggs caught (in terms of weight) to the biomass of the spawner (as the reproductive biology and the sex ratio of the species are available), and then estimate the MSY of the stock.
I wondering whether such an alternative approach is appropriate and valid for this purpose, and/or whether there are any other better approaches that can be used to estimate the possible sustainable yield of the fishery?
Any of your suggestions will be greatly appreciated.
It is a really interesting question. Using AEP method to estimate SSB looks a good alternative, although you would need adult and juvenile fish biological information to estimate maturity ogives as well as fecundity. On the other hand, to know the sustainability of the fishery, the impact of egg catches on recruitment should be estimated, so, you would need recruitment estimations or mortality rates (M and F) of eggs, larvae an pre-juveniles... There's no simple and easy answer, but exciting question. I will discuss about with my group colleagues and give you more opinions.
Dear Rosario: Thanks for the suggestion. We do have a good estimate of the fecundity and the sex ratio for the species. Thus, it is easy to convert egg biomass to the biomass of the spawners. The question was whether it is appropriate to further use this biomass to estimate the MSY of the stock if the efforts also were available. What I thought was that if the MSY of the stock (and an equivalent MSY for the egg) can be estimated, it could, at least, provide me some idea about what the level of the TAC need to be set for preventing a possible overexploitation of the resource.
Any further comments will be greatly appreciated.
This is a very interesting question. It seems to me it would be very valuable to know the percent of eggs harvested. Another approach may be to estimate the the coverage of floating algae, which could potentially be done using the Floating Algae Index (FAI) which can be obtained using satellite data. There would need to be a lot of assumptions made, but you could possibly obtain a rough estimate of "fishing" egg mortality by comparing the areal coverage of floating algae to the coverage of fishing mats. This might give you another approach to estimating of spawning biomass as well. Then using additional estimates of juvenile mortality (with the species I worked with there aren't truly flying fish larvae as they are born with the full compliment of fin rays) and adult mortality you may be able to improve your model. I have some "larval" daily growth data for a Gulf of Mexico species (using otolith increment analysis) which I doubt will have any practical use, but if you want to look at it as sample data, I could provide it for you. I also have some flying fish references that may be useful.
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