Hi Jeewantha,

As a general rule, fishery health could be estimated from different arithmetic models. The main inputs to these models may be number per catch, sexes, weight and length parameters . Some use ecological parameters as well. The outputs contain natality and mortality rate balance or net production which indicate the health level of fishery.

The attached article may contain helpful information.

Best wishes

http://www.vims.edu/library/theses/Hewitt08.pdf

Sri Jeewantha,

You can compare similar data with that of catches of same species in other parts of the world, through which you can get some idea of health of the fishery.

Dr. Salah M. Najim. Thank you for your answer. I will look into that dissertation and see if there is something there that can be applied to my research.

1. water quality parameters

2. heavy metals 

3. find out the significance between the abiotic and biotic parameters using Pearson correlation matrix

In my opinion you should evaluate different parameters such as physiological parameters of the species , ecological parameters as well...

Hi, maybe you should evaluate biotic parameters of the target species, mortality, fecundity, cacthtability and some community parameters if you have species by catch, and statistics about catch a long 10 years .

Jeewantha,

I think that you need to refine your questions before they can be answered.

"Fishery" used to mean something that human beings did to turn wild aquatic life into seafood. Over the past 20 years, the word has been misused to mean an resource that someone exploits, instead of the exploitation. You say that you are interested in the catch but that is the interface between the resource and the fishing. Are you interested in the crabs, the crab catch, the human endeavour of catching the crabs, all three of those, or something else?

"Health" properly refers to the medical (or veterinary) condition of an individual but it is commonly misused with reference to a living population, a single business corporation, an entire national economy or any other unit that interests someone. Unfortunately, while each of us thinks we know what we mean when we misuse the word, it is likely that we are all confusing one another. When you wrote "condition, quality of life" of the catch, it suggests that your focus is on the veterinary state and nutrition of individual crabs but that is entirely different from the "health" of either the resource or the human fishery endeavour.

The techniques to be used your assessment will be utterly different if your interest is in, say, the individual health of crabs, the conservation status of the crab resource or the socio-economic viability of crab harvesting.

In case you are interested in the physiological side of health of fish, fish populations, stocks, I recommend looking into this book:

Lloret et al. 2014, Condition and health indicators of exploited marine fishes, Wiley Blackwell, 247 pp.

Jeewantha, just follow Trevor's advice. He's is the right way to go.

good question. once you want to establish the health of a fishery, the likely scenario is that the fishery has been in existence for some time already, and that it is of sufficient social and economic importance, that looking into its health becomes important. therefore, you should be able to look back in time, and to establish what and how much fish was caught in the past. parameters of importance are CPUE (catch per unit effort), species composition, and size frequency of individual species in the catch. if these can be etsablished, you can do a trend analysis, and see how these evolved over time. if trends are declining, you will gain a sense that the fishery might not be doing so well, and then research into species-specific indicators, such as size/age-at-reproduction become key to understanding as to how individual species in the fishery will be affected if trends continue unabated. if trends are stable, this is a clear indication that the fishery is healthy. of course exogeneous factors - e.g. local pollution events - must be taken into account; a fishery is never evolving in isolation of other sources of impacts. if you cannot lay your hands on historic catch data, then chandravadan trivedi's approach above is your next best option, comparing your fishery to the most similar ecosystem for which healthy/sustainable exploitation rates have been established.

Jeewantha, I suggest you align your work inline with the suggestions made by Gilles E. Bosch. You are more probably interested in the condition factor (CF) of the individual of population of these crabs. The FC is an indicator of the well being of the fishery. Its a means through which detail understanding of the health status, growth pattern and other wellbeing indicators are appraised and understand in a wild fishery that is under exploitation and can independently reproduce. The CF is a function of so many factors, including natural decimating factors like diseases and pests. Ecological factors also affect the CF status of an individual within the crab population or the entire crab population. I hope this brief opinion will be helpful.

Gilles,

I do not like to respond negatively to suggestions made by others but, I regret, yours are not simply wrong but dangerous. You have echoed mistakes of half a century ago that were comprehensively debunked in the 1980s.

I agree that examining CPUE, species composition and size frequency is an important first step (if Jeewantha's interest is in resource conservation). However, CPUE is a very poor indicator of resource abundance or biomass and its stability is often a very misleading, erroneous "indication" of a stability of the resource that does not exist. Species and size compositions are more sensitive indicators in some fisheries but not in all. Yes, it is worth looking at trends in such data but nobody should suppose that stability in the numbers is a firm indication that all is well.

Conversely, when a fishery is first developed, we expect abundance and biomass to fall dramatically -- often by something between a third and two-thirds. That is the "fishing up" or "fishing down" that theorists have discussed since the 1930s. In the real world, there are also ecological interactions that fishermen respond to, so the initial depletion of an original resource species can lead to a  shift in the composition of catches, as effort concentrates on some alternative that is increasing in abundance to fill a fishery-created void in the trophic structure. In short, if trends in the basic indicators are seen, it does not necessarily show that anything is wrong, just that the resources and the ecosystem are changing from a "virgin" state to one that can support sustained exploitation.

Which leads to a more general point: Determining the status and prospects of a fishery is neither easy nor simple. Far too many people have thought that it is both and that goes a long way to explain the mess that so many fisheries are in today.

Dr. Trevor. Thank you for your answer. There's not much historical data for the fishery. In fact it's quite new. It started in 2009 after the civil war ended in the North.

I've been gathering data on catch composition, and size frequency on several locations in the fishery. Hopefully something useful comes out of the research.

trevor,

i could not agree more with what you say (save your opening paragraph), and i do not take any of your points as a negative to my points. everything you say is absolutely correct.

however, i posited at the beginning of my argument that the fishery being looked at had been around for a long time already, so that the effects of fishing down into a virigin biomass is not what we would be lookin at and detecting in trends - but indeed, trends we are looking at are trends in a mature fishery where ecosystem dynamics have adjusted, as well as fishers and their techniques. in a macro kind of way. and yes - i also agree that there is no one-size fits all approach, and a more specific question would have helped - as i believe you pointed out in your original answer (if i remember correctly).

the other point, which i did not make, and which comes from my experience of working in developing countries (only - throughout my entire career), is that there is salvation in keeping things simple and real - albeit cutting a few corners - but functional. you can answer basic first questions relating to fisheries health in a mature fishery by looking at trends in the factors / indicators i mentioned, and that is an important first step. specifically in situations where resources of government departments or other social partners (e.g. NGOs) are very limited. and such situations do characterise many fisheries today.

there is no limitation in the sophistication you may want to add later on - especially if unlimited in the amount of cash on hand to investigate. in real life scenarios though, it is often the other way around, and we do not investigate because we think we do not have the ability (cash and HR) to do so. in this sense - and i do not ever indulge in pushing my own research - i do encourage Jeewantha to download an read my 2000 FAO paper on the Samoan Student Census, and to see how these indicators i am suggesting can be collected in resource deficient environments, and contribute to gaining a better sense of what is happening in standing, developed (i.e. not new) fisheries.

Condition factor, also population dynamic studies...