Fisheries Ecology - Science topic

Hi Muhammad,

On top of the reference suggestions from my colleague Martin Bélanger, I would suggest to look at this as a simple log10-transformation of both MASS (M) fitted as the response variable, and that of LENGHT (L) as a dependent variable. If all your sampled fish come from a same population, than you can use a simple linear regression model to relate log10(M) to log(L), which should normally exhibited a high R2 value.

Here is an example from this R guide (in French) that I've written, which you can freely download at:

and that Martin has actually reviewed prior to its publication.

So, the example using MASS and LENGTH data from Arctic charr (Salvelinus alpinus = saal) that were sampled in Salluit, Québec, Canada, in 2019, referred to as "saal_SALLUIT_2019.txt" is detailed below.

The mass-at-length relationship can be viewed at p. 200 of the R Guide referred to above.

These data are here attached in a .txt format file. MASSE is for MASS (g), and LF is for FORK LENGTH (mm)

You can import this file into R with the read.delim() function, as follows with "slashes" (and thus not "backslashes"):

saal_SALLUIT_2019<-read.delim("X:/xxx/xxx/xxx/saal_SALLUIT_2019.txt")

The same (basic) figure as above (p. 200) can be obtained with:

plot(saal_SALLUIT_2019$LF, saal_SALLUIT_2019$MASSE)

You can then log10-transform both MASSE and LF as follows within the same dataset (or rename it, your choice):

saal_SALLUIT_2019 <- transform(

saal_SALLUIT_2019, LOG10M = log10(MASSE), LOG10LF = log10(LF))

And then fit a simple linear model. Using summary() at a same time allows you to directly get the model output instead of asking for it in a second step.

summary(m.saal_SALLUIT_2019.lm <- lm(

LOG10M ~ LOG10LF, data = saal_SALLUIT_2019))

You can then get your 95% confidence interval (CI) for your parameter estimates (a and b) at the log10 scale as follows:

CI95 <- confint(m.saal_SALLUIT_2019.lm)

CI95

Extract your lower and upper CI95 limits (LL and UL, respectively) for "a" your intercept and "b" your exponent from this CI95 object:

LL_a <- CI95[[1]]

UL_a <- CI95[[3]]

LL_b <- CI95[[2]]

UL_b <- CI95[[4]]

You can then back-transform your LL and UL of each paramaters (a and b) at the response scale as 10 elevated at "value of parameter", for instance for the 95% CI lower and upper limits of b:

10 ^ LL_b

[1] 1309.037

10 ^ UL_b

[1] 1682.296

You now have your 95% CI for "b".

Note that back-transforming from the log10 scale to the response scale generally requires to correct for this (i.e., to use a correction factor).

The FSA package allows you to do this with its logbtcf() function and the correction factor obtained will be stored as "cf" below:

cf <- logbtcf(m.saal_SALLUIT_2019.lm, 10)

cf

[1] 1.003403 ## not too much of adjustment to apply, but still.

***corrected 95% CI limits for parameter "b"***

10 ^ LL_b * cf

[1] 1313.492

10 ^ UL_b * cf

[1] 1688.021

Hope it helps!

Cheers,

Julien

You are correct, visual sorting gets increasingly difficult as the particle size gets smaller. The sizes of MPs that you are able to pick out of your sample first comes down to what you can see, and that is often dependent upon the magnification abilities of your microscope. And there can be a fair amount of error associated with that as MPs often look like other things (e.g., diatoms). Adding additional techniques before visualization can help a lot.

First is the digestion of the tissue. I have tried both KOH and H2O2 + heat on fish tissues and found them both to be effective. I typically use H2O2 at 65C for a few of hours with periodic agitation, depending on the size of the tissue sample. Karami et al. (2017) has a nice paper on different types of digestions. Next is separation from the surrounding media. If you are interested in separating by polymer type, then you can consider a density separation. Li et al. (2018) provides a good method. Just know that some of the chemicals used can be a little difficult to handle and particle size can impact buoyancy. The latter might be solvable by adding centrifugation (see Nguyen et al. 2019). You mention filtration, and I would say that is the most common method. There is some discussion about how to best filter samples to get the most MPs while avoiding contamination. While not the only one, Cai et al. (2020) addressed that subject recently. Personally, I think that filters are a good way to go if your MPs are large enough to be caught by it. You should consider passing the digestate and subsequent filtrates through multiple filters with smaller and small pore sizes so that you you don’t clog filter pores and when you get to the smallest particles large bits aren’t obscuring the view of smaller particles. Nanoplastics are still a big problem. The Nguyen et al. (2019) study says that their technique is able to separate those too, but I haven’t tried it yet. Its generally agreed upon (as of now) that there is no one good method to separate out the really small nanoplastics. And if you think you have a separation method, once they get that small, the only way to verify if you got any is by using an electron microscope (maybe uFTIR…very much maybe). That’s one of the reasons most people purchase fluorescent NPs to use in their exposure experiments. Next is the Nile red staining that you mentioned (I’m assuming you are using protocols from Maes et al. 2017 and Shim et al. 2016?). I certainly see this as one of the more commonly used methods to differentiate MPs from their background. And, if your microscope has enough resolution, you should be able to see particles <500um. Considering that you are using shrimp tissue, you should determine if you will get autofluorescence within the same wavelengths as the stain. I also recommend reading Meyers et al. (2022); they have some interesting ideas about using Nile red that I look forward to trying. Stanton et al. (2019) proposes the use of DAPI as a costain gives better results. And as the previous responder mentioned, FTIR has the final say in whether something is a plastic or not, and what kind it is. If it is possible for you to do on at least a subsample of what you separate from your sample, then it will make your study stronger. Regarding tissue type, I think that has more to do with your question. When dealing with aquatic organisms, exposure route should be carefully considered as it can be inhalation, dermal, and/or ingestion. Particle size typically determines if an how a particle can translocate through the body, and not all tissue types are equally permeable. The muscle seems like generic sort of tissue to look at, not in a bad way though. Would it be possible to collect hemolymph?

I’m not sure how much I helped to solve your problem, but I hope I at least gave you a few more directions to look in.

Good luck!

- Melissa

Cai, H., et al. (2020) Microplastic quantification affected by structure and pore size of filters. Chemosphere 257, 127198. http://doi.org/10.1016/j.chemosphere.2020.127198

Nguyen, B., Claveau-Mallet, D., Hernandez, L. M., Xu, E. G., Farner, J. M., & Tufenkji, N. (2019). Separation and analysis of microplastics and nanoplastics in complex environmental samples. Accounts of chemical research, 52(4), 858-866. https://doi.org/10.1021/acs.accounts.8b00602

Karami, A., et al, (2017) A high-performance protocol for extraction of microplastics in fish. Science of the Total Environment 578, 485-494. http://doi.org/10.1016/j.scitotenv.2016.10.213

Stanton, T., et al. (2019). Exploring the efficacy of Nile red in microplastic quantification: a costaining approach. Environmental Science & Technology Letters, 6(10), 606-611. https://doi.org/10.1021/acs.estlett.9b00499

Meyers, N., et al, (2022). Microplastic detection and identification by Nile red staining: Towards a semi-automated, cost-and time-effective technique. Science of the Total Environment, 823, 153441. https://doi.org/10.1016/j.scitotenv.2022.153441

Li, L., et al., (2018). A straightforward method for measuring the range of apparent density of microplastics. Science of The Total Environment 639, 367-373. http://doi.org/10.1016/j.scitotenv.2018.05.166

Maes, T., et al. (2017) A rapid-screening approach to detect and quantify microplastics based on fluorescent tagging with Nile Red. Scientific Reports 7, Article number: 44501. http://doi.org/10.1038/srep44501

Shim, W.J., et al. (2016) Identification and quantification of microplastics using Nile Red staining. Marine Pollution Bulletin 113, 469-476. http://doi.org/10.1016/j.marpolbul.2016.10.049

Suhad Mohammed

Thanks and regards

Dear Benoit,

If you are comparing your sampling sites, I would suggest using Dunn's tests. Dunn's tests work very much in the same way as a Kruskal-Wallis test (a non-parametric equivalent of the ANOVA test that does not assume normal distribution or equal variances) and is great for small sample sizes. However, unlike Kruskal-Wallis tests the Dunn's tests allow for post-hoc pairwise comparisons. There is an R package that allows you to perform Dunn's tests very easily:

https://cran.r-project.org/web/packages/dunn.test/dunn.test.pdf

Hope this helps!

Best wishes,

Dan

Follow

Hi Kent,

If you are interested in capturing live specimens with non-destructive methods then your best bet is to use traps/pots and/or suction (or slurp) guns. We also found that small nets made of clear plastic were very useful in capturing small wrasses on coral reefs. One of the best ways to capture small wrasses on reefs is with slurp/suction guns made of transparent acrylic. Papers that use these collecting techniques usually do not describe in detail how they have actually built their collecting devices. If you go to Google Scholar and search for some of these terms you’ll find a lot of information. You may find these of some help:

http://www.ices.dk/sites/pub/CM%20Doccuments/1993/B/1993_B22.pdf

Slurp or suction guns:

https://patents.google.com/patent/US3486264A/en

https://patents.google.com/patent/US3231997A/en

https://patentimages.storage.googleapis.com/a5/0d/cd/19a1135f20c2d3/US3965608.pdf I hope this is of some help.

Tomas

Here is another.

Schloesser et al. 2012. Heterogeneous detection probabilities for imperiled Missouri River fishes: implications for large-river monitoring programs. Endangered Species Research 16:211-224.

Here are recommendations for bottomfish:

I just need the price of a 6" diameter 1 meter long...fresh buy...store value.

Thanks

see

Classic bite lesion either from a lamprey or a cookie cutter shark. In this case it would be the lamprey. Key signs are the perfect circular outline, the lack of inflammation around intact skin outside the lesion and the healing of the floor of the lesion. Think about the alternative - an infection which results in an open wound will be much larger than the wound, and will interfere with the healing process.

Hi James,

sounds like you want to do a multi-species approach. Fishing with different nets by different people, especially gill-nets, may make things complicated. Do you have any possibility for capture-recapture experiments? Are the species you want to investigate suited for that? Do you have any time series of your data? Or you may think about catch-depletion methods, if that is feasible, a brief description for a start is found here: http://derekogle.com/fishR/examples/oldFishRVignettes/Depletion.pdf.

I don't know PASGEAR, but from its description it sound quite adequate. I also once worked with FiSAT II from FAO, but probably you know this already? FiSAT is better suited for analysis than for data storage. For analysis there are also plenty of R packages available, maybe fishR would be good. At least it's free, even though you might need people who know how to work with it.

Anyway good luck with your campaign!

Dear Emma Quinlan

please check the resources

animal-world.com › Aquarium Tropical Fish › Puffer Fish

badmanstropicalfish.com › Main Index › Detailed Fish Profiles › Miscellaneous species

Thank you Nirmala. 

Carasobarbus fritschii

I think you need to contact with colleagues from Institute Grigore Antipa Constanta.

hello

i'm pretty sure that it's a Spondyliosoma cantharus with a dark "fur" typical of individual in shadow area, or at night

here you'll found a link to an atlas we have published on fish post larvae and some juvenile in northwestern mediterranean.

page 141 you'll found the species

all the best

romain

Why do you want to determine (temporal) variation of fishing effort allocation in the short-term? It is a study about efficiency- skipper skills? Do you have any environmental variables that could explain variation in fishing effort allocation? Or catch yield per fishing site? Maybe you can contrast hot-spot analysis -weekly- to define variation of fishing effort allocation at that temporal scale…

Good luck!

HI Dan,

Thanks for links - I hadn't found those yet. Here's a couple more that use N-mixture:

and another one that I've attached.

Our manuscript has just been sent out for review - so hopefully you'll see it fairly soon.

Thanks, Austin

Yes, there many marine fish species eat anchovy, as sardinella aurita , scomber japonicus, Etrumeus teres. this in egypt, you can read the paper food and feeding habits of roundherring etrumeus teres in the egyptian mediterranean sea,  by Alaa Osman and Mahmoud Farrag, els

You can have at Derek Ogle website.

I think you can find what you need but you also need to be able to work in R.

Thank you

Hi Evie,

I've attached some documents that might be helpful ?

- the report inbo.r.2011.38 is in Dutch but has an English summary. The attachment in this report describes a couple of examples (=Bijlage 3: translated: "solutions for fish migration at pumping stations") --> page 73 to 80. These examples are in Dutch too but you can definitely find key words here + 'links to solutions' are given.

- In the Netherlands: try and search on 'STOWA' and 'pumping stations' / 

+ fish flow innovations

(FYI I've attached 2 papers)

Hello Federica,

Here is a useful link i use all the time to look for possible software programs to use for different scenarios in population genetics. In the section "Population Assignment", you should find something you can use.

Good luck

One example would be the Konijnendijk et al. (2011) study of Lake Victoria cichlids in International Journal of Evolutionary Biology (http://dx.doi.org/10.4061/2011/616320).  An early community genetics analysis, published by Wares (2002) in Molecular Ecology, also included teleosts (DOI: 10.1046/j.1365-294X.2002.01510.x)

Cuando se impulsan nuevas pesquerías de invertebrados marinos frecuentemente se centran en especies para las cuales existe poca o muy limitada información tanto en los aspectos biológicos como de la explotación.

Para especies de invertebrados bentónicos de nula o escasa movilidad se recomiendan los esquemas RZP (Rotación de Zonas de Pesca), este esquema eco-sistémico trata de lograr el máximo rendimiento sustentable, dividiendo el área total de pesca en sub-áreas, preferentemente de igual abundancia, para que sean explotadas secuencialmente en el tiempo y permitir la recuperación del stock en las zonas no explotadas a través de la reproducción, crecimiento y reclutamiento. Anudado a lo anterior el manejo pesquero a través de un esquema RZP, constituye una estrategia precautoria, debido a que estos esquemas ayudan a mitigar los efectos de la sobrepesca del crecimiento y del reclutamiento.

Te recomiendo consigas el siguiente artículo: Caddy, J. F. (1993). Background concepts for a rotating harvesting strategy with particular reference to the Mediterranean red coral, Corallium rubrum. Marine Fisheries Review, 55(1), 10-18.

Espero te ayude mi respuesta. Saludos cordiales.

As Daniel says, fins will tend to grow back, so fin clipping should only be viewed only as a short-term marking method. Eel fins can get somewhat ragged, so positively identifying the mark could be tricky. Regardless of whatever marking method you use with eels, you will need to anesthetize the fish (too difficult to handle eels while marking without anesthesia).  Other marking methods used with eels include freeze branding, elastomer injections, and to some extent dye marks). PIT tagging (if you can afford it) is becoming the most popular; long-term mark: relatively rapid, positive individual identification, etc.  Email me if you would like more info/details on marking methods for eels: aharo@usgs.gov.

Length infinity, weight infinity, length at age, t0, Probability of caputre, recruitment pattern, natural, fishing and total mortality, exploitation rate

The main species caught as bycatch is the common hake (Merluccius hubbsi).

You can read more:

1) Fish bycatch in the Patagonian shrimp fishery Pleoticus muelleri María E. Góngora, Nelson D. Bovcon y Pablo D. Cochia. Rev. biol. mar. oceanogr. v.44 n.3 Valparaíso dic. 2009 http://www.scielo.cl/scielo.php?pid=S0718-19572009000300006&script=sci_arttext

2) Argentine red shrimp off-shore (English) , Fishery Improvement Project (FIP) http://cedepesca.net/promes/shrimp-and-lobster/argentine-red-shrimp-off-shore/

Best regards,

No, in fact I would suggest the simple length-at-observed age observations would be superior to back-calculations. One problem with back-calculations is that it over-emphasizes older fish because they will have more back-calculated lengths at ages. This can be handled statistically using mixed effects models, but these models are inherently more complex and harder to explain to non-statistical persons. Another problem with back-calcs relates to issues arising from Lee's and Reverse Lee's phenomenon (not fixed by using observed ages, but effect potentially lessened). So, bottom line is don't feel the need to back-calculate if you have a good sample size of observed lengths at age.

Some additional elements/ideas that perhaps you should consider in analyzing this complex relationship:

(1) Direct benefits of tourism from fisheries (in terms of provision of fresh fishing products to taverns, hotels etc.)

(2) Indirect benefits of tourism from fisheries, like the traditional "colour" of fishing villages and ports that adds to their image and attracts tourism.

(3) Direct benefits of fisheries from tourism, like rise in demand and in prices of fishing products).

(4) Diversification of fisheries like development of fishing tourism infrastructures, funding of vessel modernization and modifications to take tourists for "fishing tours" on-board coastal fishing vessels.

(5) Competition between fisheries and tourism for space in the coastal zone (both terrestrial and marine).

Best regards,

Vangelis

I think you need to consider about the feeding behavior of both

Aside a precautionary approach, I suggest to employ some kind of adaptive management. This is not easy and could be very expensive to obtain continuos data series, but you can include fisher's involvement.

Please check this link.

"Only by mapping ocean wealth and demonstrating fish

production, erosion prevention, mitigation of storm-related

risks, recreation, tourism and so many other services can

decision makers value ocean habitats for what they are truly

worth to society, and all that is at risk should they fail."

As they are spiny, there might be some physical injury caused by the spines if you keep them in a net cage at crowded condition which eventually increases the mortality.

When man lives in one place and makes part of that ecosystem he has the right to use that space as any other animal. But tourism is most of the a predatory relationship. We should change this relationship and limit or prohibit avenues by the sea shore, lights, buildings block the wind, etc. 

You´re welcome!

Good luck with your studies!

The definition of coastal small-scale fisheries is very important when we design management plans for the coastal ecosystems. The coastal fisheries encompass basically the areas which are accessed by the traditional and motorised fishermen who operate their boats which are mostly up to 10 hp and a length of  5-8 m. Thus first and foremost, there should be effective legislation to stop illegal

1)Thus first and foremost, there should be effective legislation to stop illegal in indiscriminate fishing in these regions.

2) Effective and continuous patrolling using patrol boats and coastal police vessels should be implemented

3) Once first two points are done, there should be prohibition to any activities which may change the general biology of fishes (migration, feeding, breeding etc.) like mining, dumping of wastes, etc. 

4) A continuous reporting system  for catch, unique observations (fish death, heavy landing) using ICT and other technological and issues between fishermen should be implemented using the community-based fisheries management

5) If already some systems of fisheries limits exist in the coastal systems (traditional and religious controls), if they found adequate, try to promote them

6) Estimate the fisheries and biodiversity of the ecosystems with rigorous sampling with participatory approach to make the fishermen understand the importance of the study.

7) The projects should be focused for long term to make an impact in the livelihood of fishermen

Stakeholders identification

what whom should  do?

1) Fisheries patrolling- state-level Departments

2) The data collection and analysis from different sources- Research institutions like ICAR

3) Reporting of fisheries data to research institutions and dept.--Fishermen community  on a weekly basis.

4)Awareness and training programmes- Research institutions and Dept.

We have a periodic closure of mechanised fishery In India and we have studied the impact of this seasonal closure and based on the study   presented a paper on the impact of periodic closure on the spawning biomass and recruitment  some of the trawl target species. There was marked improvement in spawning stock biomass and recruitment numbers

The key is to have a good mutational model for whatever regions you type. Then you can apply that model to coalescent simulation, of some other means of simulating data, to generate different expectations of your data under different models you want to explore / test / compare.

Single loci systems (e.g. mtDNA) would be a poor choice as  its genealogy is usually only weakly constrained by the demographic history, so logically it only contains very limited information on that demographic history. BEAST  is very good at squeezing information out of mtDNA data, but please remember that it is so elegant precisely because it assumes a single population model.

This frustration has lead many into the murky and pseudo-scientific world of interpretative phylogeography, and a collapse in their scientific credibility.

If you have many thousands of genomic loci (SNPs, STRs) there are plenty of clustering-based approaches that will sharpen your intuitions about underlying population structure. FineSTRUCTURE is pretty good, and has a time component, and for pretty plots you could do PCA / ADMIXTURE / others mentioned Temim Deli above. But do remember that most of the genome-wide analysis methods don't allow you to estimate parameters for, or compare different bespoke models.

Luis,

Much depends on what you mean by "successful" and come to that what you mean by "management". If you are looking for examples of success of "modern" (i.e. government-centred, science-based, conservation-oriented) fisheries management, you will have to search long and hard, whether you include all fisheries or just the small-scale ones.

On the other hand, human beings managed their fishing, more or less successfully, for millennia before the advent of large-scale, offshore fishing -- during an era when data (in the modern sense) did not exist at all. Ever-evolving variants of the systems used in the distant past have continued to be employed, still with some success, down to the present time, though they are being gradually swept aside by governmental imposition of the "modern" form of management (designed to address the problems of the large-scale, offshore fisheries -- though conspicuously ineffective for that purpose).

The best introduction to the topic is probably the ethnographic literature on the Polynesian, Micronesian and Melanesian peoples. There is also a substantial literature on the lobster fisheries of Maine, which provides insight into an application in a modern, highly-developed nation. Beyond those, you can just delve into the fisheries social-anthropology literature. Not all is directly relevant to the management of fishing but community-based management must be founded in communities and hence their structure must underpin the success (or failure) of that management.

Trevor Kenchington

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.

here are a few things that i would consider also in formulating a hypothesis; a) if there was an instantaneous mass mortality of fish, it would suggest that there was an out-of-the-ordinary event that triggered it. regular (illegal) gold mining might not be that event- unless there was an extraordinary spill event that took place. b) there is only one species of fish killed, not others (?) - what sets these fish apart from other fish in biological terms (?); c) what is farming like in the area and the catchment basin, and have you considered looking into pesticide run-off (e.g. DDT) which is also a known cause for massive fish kills.

In some countries, fishermen are shy to provide truthfully their catch data because they may be used by their authorities for taxation purpose, such as income tax, or by monopolistic fish-buyers to whom the fishermen are obliged to deliver all their fish. In such cases, the best way is to create a system, by which such data are supplied to fishery statisticians anonymously.

The most famous eastern Atlantic example is from the 1930s, when the Dutch build the afsluitdijk http://en.wikipedia.org/wiki/Afsluitdijk. Researchers at the time noted that for up to 3 years after the closure of the Zuider Zee, the herring returned to spawn and used the dijk as they could not reach their traditional spawning sites or spawning substrate.

Creating spawning habitat below dams is occurring for salmonids in tributaries to the Sacramento and San Joaquin rivers in California. This tends to occur below dams in lower elevation areas, outside of historic spawning areas. There remain limitations to their long term benefits due to warm water temperatures in the Fall when chinook salmon want to spawn, and fish passage may be another consideration in the long term for fish reaching spawning grounds with suitable water quality. Monitoring and research articles are available from this type of activity on the American River, Mokelumne River, and Merced River. You should be able to find it with a good search engine.

Even lethal and labor intensive methods can be unsuccessful for distinguishing mature from immature individuals, like gonadal histology. The main problem is that immature fish have the same composition of gametes with regressing, resting or very early regenerating fish (all these are mature phases): females from all these phases contain only primary oocytes. Therefore, simpler indices like the gonosomatic index or the macroscopic appearance of the gonad should again be unsuccessful. Some workers use other characteristics like ovarian wall thickness or the prevalence of atretic follicles. Blood tests for steoid composition (e.g. estradiol levels) could be one possible solution but then your method will not be simple any more. These difficulties make simple and non-invasive tests for the maturity status almost impossible.

Alex

here is an approached used in Western Australia

See: The invasion of Saurida undosquamis (Richardson) into the

Levant Basin - an example of biological effect of inter-oceanic

canals. Fish.Bull.(USA), 72 (2):359-373. (Ben-Yami, M and T.Glaser), 1974. Describes fluctuations in 2 alternating fish populations relative to climate fluctuations.

Any fisheries management plan needs to have fishery biologists in evolving the scheme of things. As far as I know,these individuals are not involved in making of such management plans.Moreover a huge amount of technical data with constant input is involved in making of such plans.In puts have to come from state fisheries departments & almost all of them are not capable of doing this.Central Research Institutes have their own limitations. Any management tool which the fishermen feels that would involve more of Governmental interference or probable loss of harvest is overtly or covertly pulled down by them. Management plans in India needs to be evolved taking all these into consideration & knowing the ground scenario.

I'm going to go out on a limb here and see if you cant try a molecular approach. If you used real time pcr you might be able to munch up the bones and identify contributing species based on species specific markers.

It would be fast, but pretty expensive.

Just a thought.

SST functions for only 2 to 3 days after the data is downloaded,beyond which it is ineffective.Certain maritime states have their own fishing rules in order to have sustainability.For e.g.Kerala doesn't allow mechanized vessels to operate within 5 KMs coastal zone.Other states do have closed fishing seasons, coinciding with fish breeding season. But the point here is the authorities can't effectively monitor any part of fishing activity,thereby leaving the area to be free for all.To compound the problem,foreign vessels say from Taiwan do fish in potential zones & get scot free - due to laxity in monitoring.Moreover in the name of catching fish wherein fish trawl is to be used,almost all the trawlers use shrimp trawl,smothering the benthic structure of sea beds.The cod end mesh size is so small that even baby fishes get caught to the extent of 80% of the total catch of the trawlers.This waste doesn't even fetch any price & being a waste,directly hits future stock.The fishermen are so cleaver that they know each of the potential fishing zones among them selves & they don't depend on any advices from authorities.

Relevance of the gear will vary among species but a good approximation is to recognise fish frequently undergo size based diet shifts associated with for example ontogeny, habitat requirements, reproductive behaviour etc. Secondly the size of fish captured varies among gears. There are huge volumes of literature on both these points. Thus a simple approximation of gear bias on diet interpretation is the size selectivity difference among the gears. Other biases include the ability to use a gear in a given type of habitat and not another e.g. soft vs. hard and rough that often impacts fish diet. In deeper trawl samples one can get both net feeding and stomach inversion due to barotrauma, the first of which adds erroneous prey, the second increases empty stomach counts. A final point, different gears return different numbers of individuals per deployment. Sample size alone will impact diet characterisation e.g detecting rare diet items vs. under characterised diets