Author Topic: Science corner: latest fish & fisheries research  (Read 39004 times)

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Offline Visenvryheid

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Re: Science corner: latest fish & fisheries research
« Reply #220 on: October 17, 2019, 12:13:36 PM »
Very interesting reading! So we got good at catching the big cob, and perhaps also better at catching the leeries (Anecdotally from the old timers the leeries were in all the haunts they are now, in the old days, but in much much larger numbers of far larger fish in the old days. The galjoen has been hammered and we have fished out the red and black steenbras.

Offline FishStyx

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Re: Science corner: latest fish & fisheries research
« Reply #221 on: October 19, 2019, 05:20:25 PM »
All the more reason to keep catch reports flowing on responsible social media like UA.  :Like:
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Offline John F

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Re: Science corner: latest fish & fisheries research
« Reply #222 on: December 18, 2019, 11:16:16 AM »
Growth Limitation of Marine Fish by Low Iron Availability in the Open Ocean


* It is well-established that phytoplankton growth can be limited by the vanishingly low concentrations of dissolved iron found in large areas of the open ocean;


* However, the availability of iron is not typically considered an important factor in the ecology of marine animals, including fish;


* Observations that show that the iron contents of lower trophic level organisms in iron-limited regions can be an order of magnitude less than the iron contents of most fish were compiled;


* Although this shortfall could theoretically be overcome if iron assimilation rates were very high in fish, observations suggest this is not the case, consistent with the high recommended iron contents for mariculture feed;


* In addition, two occurrences among fish living in iron-poor regions that would conceivably be beneficial given iron scarcity are highlighted: the absence of hemoglobin in Antarctic icefish, and the anadromous life history of salmon;


* Based on these multiple lines of evidence, it is suggested that the iron content of lower trophic level organisms can be insufficient to support many fish species throughout their life cycles in iron-poor
oceanic regions;


* A global satellite-based estimate of fishing effort was used to show that relatively little fishing activity occurs in high nitrate low chlorophyll (HNLC) regions, the most readily identified iron-poor domains of the ocean, particularly when compared to satellite-based estimates of primary production and the observed mesozooplankton biomass in those waters;


* The low fishing effort is consistent with a low abundance of epipelagic fish in iron-limited regions, though other factors are likely to contribute as well;


* The results imply that the importance of iron nutrition extends well beyond plankton and plays a role in the ecology of large marine animals.



pdf available.
Reference:
Galbraith, E. D., P. Le Mézo, G. S. Hernandez, D. Bianchi & D. Kroodsma (2019). Growth limitation of marine fish by low iron availability in the open ocean. Frontiers in Marine Science, 6: 509. doi: 10.3389/fmars.2019.00509
« Last Edit: December 18, 2019, 11:16:44 AM by John F »
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Offline John F

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Re: Science corner: latest fish & fisheries research
« Reply #223 on: January 20, 2020, 09:21:28 AM »
Life history, distribution and seasonal movements of a threatened South African endemic seabream, Chrysoblephus gibbiceps
* The red stumpnose Chrysoblephus gibbiceps (Sparidae) is a South African endemic seabream that has been severely depleted by fishing.


* A total of 678 C. gibbiceps were sampled by line and trawl fishing for a study of their morphology, age, growth, reproduction and diet. In addition, catch records from three time-periods since 1897 were interrogated for distribution patterns and movement behaviour.


* The sex ratio was 1.5:1 in favour of males. The length–weight relationship, W = 9.32 × 10−5 LF 2.811, indicates hypoallometric growth.


* The bulbous head of large males is a secondary sexual characteristic.


* A von Bertalanffy growth model was fitted to age data obtained using otolith analyses: LF = 429.9 × (1 – e−0.113(t – (−3.799)).


* The maximum recorded age was 48 years, which is among the highest in seabreams, though the species matures after only 3 years.


* The gonadosomatic index (GSI) of ripe females (4.5%) was comparatively low, and the two-month-long early-summer spawning season was short compared with that of other sympatric seabreams.


* The very low GSI of ripe males (1.6%) suggests courtship battles and polygamy.


* The species feeds over low-profile reefs and consolidated sediments.


* The principal prey are ophiuroids.


* Although its trophic level is 3.7, C. gibbiceps has a low-nutrition diet.


* Historical and current catch data confirm a distribution from Cape Point (southeastern Atlantic) to southern KwaZulu-Natal Province (western Indian Ocean).


* There is evidence for localised migratory patterns, now partly lost due to severe population depletion.


* Whereas protogyny and resident behaviour have been suggested as traits that render seabreams vulnerable to fishing pressure, C. gibbiceps is a shoaling gonochorist that has collapsed due to fishing.





pdf available.

Reference:Attwood, C. G., M. E. Dawson, S. E. Kerwath & C. Wilke (2019). Life history, distribution and seasonal movements of a threatened South African endemic seabream, Chrysoblephus gibbiceps. African Journal of Marine Science, 41 (4): 395-411.
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Offline FishStyx

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Re: Science corner: latest fish & fisheries research
« Reply #224 on: January 20, 2020, 09:35:09 AM »
Thanks Marcos... And thank you for keeping this thread going.


The sex ratio... I wonder if that's actual or of those caught... Any idea?
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Offline John F

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Re: Science corner: latest fish & fisheries research
« Reply #225 on: January 20, 2020, 09:40:59 AM »
The sex ratio is of those 678 fish sampled. It is usually assumed that the sample is random (unless there's evidence that points otherwise), and thus indicative of the actual situation.

That's why sample size is crucial... and you will always hear biologists (or any scientist for that matter!), cry over sample size and claiming more studies are needed (well, also need to pay the bills heheheheh)
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Offline FishStyx

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Re: Science corner: latest fish & fisheries research
« Reply #226 on: January 20, 2020, 09:44:13 AM »
I was wondering if males are just more stupid (and prone to getting conned by anglers) than females...  w;k
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Offline John F

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Re: Science corner: latest fish & fisheries research
« Reply #227 on: January 20, 2020, 12:16:44 PM »
Well, usually males of any species are more stupid :hyst: ...  but don't really think it matter in this case...

However, in some species (the hammerhead shark for example), are notorious for large aggregation of females .... and these could potentially be risky in terms of wiping out females or males...
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