Science corner: latest fish & fisheries research

[FishStyx]

30 tons of awesome fishing power... The stuff that dreams are made of. 

[Visenvryheid]

  Also from me, thanks! Awesome..the spawn from the 30ton breeding machine is probably what makes it into the transkei rivers..You guys seen that video of the migration they do up the Mtentu river? (or used to do this year Sanral stuffed up the estuary in building the new N2 bridge and the GT's never came, if and when they try force the mining through of the coastal dunes then it will be a bugger for the nurseries for these fish)

https://www.youtube.com/watch?v=GKK93VAM-_w

Big F'ing fish ;) I wonder if the aggregration studied in your post are one and the same that do the migration/pilgrimage to where they grew up as little marauders in the TK rivers?

http://aidc.org.za/famous-mtentu-river-damaged-by-up-stream-sand-from-sanrals-n2-mega-bridge-project/

Recent Mtentu news..

[John F]

Evaluating the effects of catch-and-release angling on Cape stumpnose Rhabdosargus holubi in a South African estuary


* Fisheries managers are increasingly promoting catch-and-release (C&R) to manage recreationally angled fishstocks;


* Despite this, there is a scarcity of information on the effects of C&R on estuarine-dependent species;


* Cape stumpnose Rhabdosargus holubi dominates the recreational fisheries catch and provides an important source of food for subsistence fishers in some temperate South African estuaries;


* The health and survival of R. holubi exposed to a C&R event was investigated by examining their physiological stress response (blood glucose and lactate), reflex impairment (reflex action mortality predictors [RAMP]) and short-term (12-hour) survival;


* Fish were captured and exposed to one of three air-exposure treatments: 0 s, 30 s or 90 s;


* Stress and health were measured either immediately (immediate) or one hour after (delayed) the C&R event;


* There was no significant difference in blood glucose between air-exposure treatments, but there was a significant difference between the mean immediate and delayed glucose levels within each treatment (F(2,143) = 81.8, p < 0.01);


* In contrast, blood lactate level was significantly higher in the 90-s treatment (p < 0.05);


* Immediate blood lactate levels were significantly lower than the delayed samples for each treatment (F = 4.29, p = 0.02; n = 169);

* Although all fish exhibited at least one reflex impairment, the RAMP score was significantly higher in the 90-s air-exposure treatment (H(2,86) = 9.73, p = 0.007);


* Also, RAMP scores were significantly lower in the delayed samples (p < 0.01);


* Although short-term mortality was relatively low (2.3%) for this species, it was highest in the 90-s treatment (7%);


* These results suggest that physiological stress is higher when R. holubi are exposed to longer periods of air exposure and that the
physiological stress of fish subject to a C&R event is best measured after a delay.


pdf available.
Reference:
Arkert NK, A-R Childs, MC Parkinson, AC Winkler, E Butler, S Mannheim & WM Potts (2018). Evaluating the effects of catch-and-release angling on Cape stumpnose Rhabdosargus holubi in a South African estuary. African Journal of Marine Science, 40(3): 235–244.

[FishStyx]

Pretty much confirms the thinking of "get the fish back in the water asap". I get quite rattled when anglers spend too much time taking photos and faffing around. But at least this also debunks the myth that the bulk of fish caught die after release. Thanks bud.

[John F]

Fifty-five-year longevity for the largest member of the family   Sparidae: the endemic red steenbras Petrus rupestris from South Africa

* A previous study that explored the age and growth of red steenbras Petrus rupestris (Valenciennes, 1830), a large sparid (family Sparidae, seabreams or porgies) endemic to South Africa and reported to approach 2 m in length, provided estimates as a moderately slow-growing species with a maximum age near 30 years;

* The stock is considered collapsed and a fishing moratorium was imposed in 2012, resulting in this species being assessed as Endangered by the IUCN;

* One consideration in addressing population status is validation of life-history traits;


* In this study, estimates of age for red steenbras from thin-sectioned otoliths were reassessed visually in terms of both the original ages and revised estimates using a different age-reading pattern;

* The revised ages exceeded the original ages by up to 30 years, with a maximum estimated age of 55 years from a well-defined otolith section that provided a basis for the revised age-reading procedure;

* Bomb radiocarbon (14C) dating revealed there was an offset in the timing of the 14C rise on the Agulhas Bank that, when coupled with considerations for regional oceanography, provided support for the revised age-reading pattern and an estimated longevity that exceeds 50 years;

* These findings were further supported by the fortuitous recapture of a tagged red steenbras that was at liberty for 22 years.



PDF available.

Refrence:
Andrews, A. H., M. J. Smale, P. D. Cowley & N. Chang (2018). Fifty-five-year longevity for the largest member of the family Sparidae: the endemic red steenbras Petrus rupestris from South Africa. African Journal of Marine Science, 40 (4): 343-353.

[Lofty]

Thanks for sharing!Wow,imagine catching a fish that's been living in the ocean for longer than I've been alive!That's amazing...should call these older fish OOM before releasing..lol

[FishStyx]

That's bloody old... Show these fish some


Thanks Marcos 

[colin]

Marcos    always enjoy your posts .     

[REEFMAN]

Interesting!! 

[John F]

Movement patterns of an endemic South African sparid, the black musselcracker Cymatoceps nasutus, determined using mark-recapture methods

* This study made use of data from three long-term fish tagging projects along the South African coastline to investigate the movement behaviour of the endemic black musselcracker Cymatoceps nasutus (Sparidae).

* From 1984 to 2016, a total of 3 430 C. nasutus (178–980 mm fork length) were tagged (with small plastic dart tags) throughout the species’ distributional range, with an overall reported recapture rate of 7.2%.


* Recaptured individuals displayed high levels of residency, moving an average of 14.8 km, with time-at-liberty ranging from 0 to 6 809 days.


* The majority of recaptures (84.6%) were made within 1 km of the tagging sites; however, some large-scale movements, of up to 528 km, were recorded.

* Although C. nasutus individuals moving greater distances were characterised by greater mean sizes (mm fork length) at time of recapture, the distances moved by juveniles were not significantly different from those of adults (p > 0.05).


* Low levels of connectivity among coastal regions were therefore expected due to the high degree of residency displayed by this species.


* Combining traditional management approaches together with a well-designed network of no-take marine protected areas is likely to be the most effective way to protect this vulnerable species.


* A lack of data on the movements of adults remains a challenge, but this could be overcome by tracking large individuals tagged with long-life acoustic transmitters.




PDF available.

Reference:Murray, T. S., P. D. Cowley, B. Q. Mann, J. Q. Maggs & G. Gouws (2019). Movement patterns of an endemic South African sparid, the black musselcracker Cymatoceps nasutus, determined using mark-recapture methods. African Journal of Marine Science, 41: 71-81.

[byrox]

don't know if this the correct place to post this  - Hi all, just wanted to know if any of you noticed the abundance of the lantern bream fish mostly on the north coast including Umhlanga Rocks as well.

I have seen fishermen catching more than their quota and this fish is coming out thick all over - some of them were in the 2 till two and a half kg weight category however its very sad to see that they are taking so many of these fish out . I saw a guy catch 16 of this and he bagged all 16 I saw another couple of guys catching around the same number as well. are these fish facing any challenges ? its my first time in my fishing career seeing this.

[John F]

First marlin archival tagging study suggests new direction for research


* Decades of billfish tagging studies have been hindered by below-par conventional tag recovery rates and high rates of premature satellite pop-up tag shedding.


* With hopes of obtaining long-term tracking data, the world’s first archival tagging study on an istiophorid was performed, by surgically implanting 99 archival tags into the peritoneal cavity of
striped marlin (Kajikia audax) off the coast of Baja California, Mexico.


* Marlin were also tagged externally with a conventional tag before release.


* Ten archival tags (10.1%) were recovered with days at liberty (DAL) ranging from 400 to 2795.


* Nine recoveries were from Mexican waters, whereas one marlin was recaptured off Ecuador.


* In total, 100% of the light stalks on the archival tags failed, with nine failing within the first 3 months of deployment; because the light data are used to estimate the geographic position of the tagged fish, tracking data were compromised.


* The absence of conventional tags on all recaptured marlin indicates that studies of marlin using conventional tags have been hindered by tag shedding
rather than tagging-associated mortality or underreporting.


* The high recapture rate and long DAL suggest istiophorid science could be greatly advanced by archival tagging if new tag designs or methods can eliminate tag failure.


PDF available.

Reference:
Domeier, M. L., S. Ortega-Garcia, N. Nasby-Lucas & P. Offield (2019). First marlin archival tagging study suggests new direction for research. Marine & Freshwater Research, 70: 603-608.

[John F]

Basically, all tagging done by recreational anglers is pretty much useless!!!!!

[FishStyx]

Basically, all tagging done by recreational anglers is pretty much useless!!!!!

I take it you are referring only to Marlin?

[John F]

Basically, all tagging done by recreational anglers is pretty much useless!!!!!

I take it you are referring only to Marlin?

Yes.

Results on other species are overwhelmingly clear and unequivocal.

[John F]

Acoustic telemetry reveals multi-seasonal spatiotemporal dynamics of a giant trevally Caranx ignobilis aggregation


* Predictable fish aggregations of commercially valuable species are particularly susceptible to overexploitation.


* Giant trevally Caranx ignobilis are ecologically important top predatory fish targeted in both recreational and commercial fisheries; however, little is known about their aggregation dynamics or susceptibility to overexploitation.


* This study employed acoustic telemetry to investigate the temporal and spatial characteristics of one of the largest known aggregations of this species over a 3 yr period in a marine protected area in Mozambique, West Indian Ocean.


* Tagged fish were monitored for between 386 and 1176 d, during which they exhibited distinct aggregative periods in austral spring and summer.


* The detection frequency of fish at the aggregation site was significantly associated with rising mean sea temperatures and the full moon period.


* Whilst at the aggregation site, fish exhibited clear patterns of diel periodicity, with maximum hourly detections recorded during midday.


* All fish exhibited periods of absence from the aggregation site between summer seasons, in which time many of them ranged across an international border for distances of between 11 and 633 km before returning to aggregate at the same site in the following season.


* These results confirm that the studied giant trevally aggregation is temporally and spatially predictable, and consistent with a transient site-specific fish spawning aggregation.


* The spatiotemporal predictability of the aggregation highlights the need for the effective management of this transboundary population of giant trevally, for which this study has provided conservation management recommendations.



PDF available.

Reference:

Daly, R.,  J.D. Filmalter, C.A.K. Daly, R.H. Bennett, M.A.M. Pereira, B.Q. Mann, S.W. Dunlop & P.D. Cowley (2019). Acoustic telemetry reveals multi-seasonal spatiotemporal dynamics of a giant trevally Caranx ignobilis aggregation. Marine Ecology Progress Series, 621: 185-197.

[FishStyx]

This has puzzled me for years... Do they have any clues as to why they do it?

For those who don't know (I didn't)... Definition of diel. : involving a 24-hour period that usually includes a day and the adjoining night diel fluctuations in temperature.

[REEFMAN]

Great info! 

[colin]

 

[John F]

Can long-term content analysis of print media be used to examine species   composition, population demography and changes in distributional range of recreational fishery species?


* Although marine recreational fisheries are socially and economically important, there is often limited funding for their monitoring and assessment.


* With South African anglers reporting catch declines for almost all targeted species and little long-term monitoring data available, novel methods need to be explored to provide managers with additional information.


* This study aimed to evaluate the efficacy of content analysis of print-media records for detecting long-term trends in species composition, size composition and distribution of selected recreational fishery species.


* Information for eight fishes captured in the marine shore-based fishery was collected from South Africa’s most popular recreational fishery magazine, between 1960 and 2009.


* During the five decades, there were shifts in the catch composition, from being dominated by slow-growing, large predators to faster-growing, large predators and lower-trophic-level species.


* There were no significant trends in the mean and maximum sizes of the dominant species, except for dusky kob Argyrosomus japonicus, which increased significantly in the maximum
size reported during the study period.


* The distributional range of A. japonicus and leervis Lichia amia significantly increased, and that of galjoen Dichistius capensis significantly decreased.


* However, it was uncertain whether these trends could be attributed to population changes, changes in angler technology and/or behaviour, or climate signals.


* Overall, this type of content analysis may provide a cost-effective method to examine changes in species composition and fish distributions over time, but, without detailed knowledge of shifts in angler behavioural patterns, it may not be as useful for understanding changes in the population dynamics of recreational fishery species.


* It is suggested that fishery-independent monitoring programmes are most suited for this type of complex fishery.



pdf available.


Reference:
Potts, W. M., T. Jordan & A.-R. Childs (2019). Can long-term content analysis of print media be used to examine species composition, population demography and changes in distributional range of recreational fishery species? African Journal of Marine Science 2019, 41(3): 231–245.