Science corner: latest fish & fisheries research

[LGF]

Crazy to think what us humans are capable of and worst is that we might never even realise the effects of our behaviour!

[LGF]

Something to think about, over how long a period was this particular study done? Reason for asking relates to seasonal baits/food.

[WalkersKiller]

Thats crazy stuff, wow!

[John F]

Something to think about, over how long a period was this particular study done? Reason for asking relates to seasonal baits/food.

According to the paper, the survey took place from late December 2013 through to the beginning of March 2014.

[LGF]

Thanx for the reply, I was just wondering what influence seasonal availability of a certain food source would've had on the study?


Would've been interesting had they conducted it over a two year period, I know funding might have been a serious issue, nonetheless if they could perhaps they might have stumbled upon a repeat of a pattern. Not sure just a thought?

[John F]

Monitoring the recovery of a previously exploited surf-zone fish community in the St Lucia Marine Reserve, South Africa, using a no-take sanctuary area as a benchmark

* Limiting accessibility to a fishing area can reduce fishing effort effectively and may therefore promote local recovery of depleted stocks. In January 2002, beach driving was banned in South Africa, thereby reducing angler access to large areas of the coastline, particularly in less-developed areas;

* In November 2001 a project had been established in the St Lucia Marine Reserve, on the east coast of South Africa, to compare surf-zone fish populations inside a no-take sanctuary zone with those in an adjacent exploited area;

* Subsequent to the ban, the aim of the project was adapted such that surf-zone fish populations were monitored for potential recovery in what had been the exploited area, located to the north of Cape Vidal, which anglers could no longer access easily, because of the
prohibition on beach driving;

* Standardised research fishing was conducted at two sites in the previously exploited area and two sites in the no-take sanctuary;

* Conventional stock-status indicators showed evidence of recovery in the four most common species caught in the previously exploited area, in terms of both abundance and biomass;

* Generalised additive mixed models were used to account for the influence of targeting specific species; however, subtle differences in habitat between the sampling sites, improved angling skill over time, variability in recruitment, and differential species-specific responses complicated interpretation of results;

* The implications of the findings are discussed in terms of the future monitoring and management of marine protected areas both within the St Lucia
Marine Reserve and farther afield.

pdf available.

Reference:

Mann, BQ, H Winker, JQ Maggs & SN Porter (2016). Monitoring the recovery of a previously exploited surf-zone fish community in the St Lucia Marine Reserve, South Africa, using a no-take sanctuary area as a benchmark. African Journal of Marine Science, 38(3): 423-441.

[John F]

Life cycle of chokka-squid Loligo reynaudii in South African waters

* This short note summarises past and current knowledge of the life cycle of chokka-squid Loligo reynaudii d’Orbigny, 1845, in South African waters;

* Prior to approximately 2010, the chokka-squid stock was considered simple and uniform, with one paralarval pool, the drift of paralarvae westwards, one main nursery area and one main, long spawning migration of adult squid eastwards, back to the main spawning grounds;

* Based on new information, this life-history scheme has been revised. Genetically, the stock is uniform; however, morphologically, it comprises three main geographic groups;

* It is proposed that the differences between the groups originate from many different paralarval events and that short (not long) migrations dominate the life cycle.

PDF available.

Reference:
Lipiński, M.R., J.S.F. van der Vyver, P. Shaw & W.H.H. Sauer (2016). Life cycle of chokka-squid Loligo reynaudii in South African waters. African Journal of Marine Science 2016, 38(4): 589-593.

[John F]

Seasonally and spatially referenced estimates of recreational shore-angling effort, catch composition, catch rates and total catch in the Goukamma Marine Protected Area, South Africa

* A roving creel survey of the recreational shore fishery along the 16.4-km coastline in the Goukamma Marine
Protected Area on the south coast of South Africa was conducted from 2009 to 2011;

* Some 838 patrols were stratified equally among months, areas and years, but intentionally biased towards weekends;

* Angler densities at Buffalo Bay and Groenvlei were 0.59 and 0.28 anglers km−1, respectively;

* Weekend densities were double to quadruple weekday densities and fishing during winter was more popular than during summer;

* Area, habitat and distance to access points explained variation in angler densities;

* Shannon–Wiener diversity in catches declined from 2.18 in an earlier (1993–2002) survey to 1.79;

* Although the order of species abundance in the catches remained largely unchanged, blacktail Diplodus capensis dominance increased to 57.3% by number, at the expense of galjoen Dichistius capensis;

* Habitat explained 27% of the variance in catch composition;

* The catch per unit effort (CPUE) for the top nine species ranged from 0.19 to 6.35 fish 100-h−1.

* The CPUE of all species, except spotted grunter Pomadasys commersonnii, declined;

* Blacktail and galjoen CPUE declined by 17% and 77%, respectively;

* The total catch estimate was 2 986 fish y−1;

* Transgressions of size limits were common;

* The results suggest that the fishery is overexploited and that catch rates are declining.


pdf available.

Reference:

Attwood, C. G., C. S. van Zyl, A. T. Lombard & C. McCagh (2016). Seasonally and spatially referenced estimates of recreational shore-angling effort, catch composition, catch rates and total catch in the Goukamma Marine Protected Area, South Africa. African Journal of Marine Science. 38 (4): 563-579.

[John F]

Assessing trophic adaptability is critical for understanding the   response of predatory fishes to climate change: a case study of   Pomatomus saltatrix in a global hotspot

* There is a growing need to incorporate biotic interactions, particularly those between predators and their prey, when predicting climate-driven shifts in marine fishes.

* Predators dependent on a narrow range of prey species should respond rapidly to shifts in the distribution of their prey, whereas those with broad trophic adaptability may respond to shifts in their prey by altering their diet.

* Small pelagic fishes are an extremely important component of the diet of many marine predators. However, their populations are expected to shift in distribution and fluctuate in abundance as the climate changes.

* A comparative study of the seasonal diet of adult Pomatomus saltatrix over two periods (June–December 2006 and 2012) was conducted and examined the available data on small pelagic fishes biomass in a global hotspot (the coastal region of southern Angola, southern Africa) to gain an understanding of the tropic adaptability of the species.

* Despite a drop (630 000 t to 353 000 t) in the abundance of their dominant prey (Sardinella aurita) in the region, it remained the most important prey item during both study periods (Period 1 = 99.3% RI, Period 2 = 85.3% RI, where %RI is a ranking index of relative importance).

* However, the diet during Period 2 was supplemented with prey typically associated with the nearshore zone.

* The seasonal data showed that P. saltatrix were capable not only of switching their diet from S. aurita to other prey items, but also of switching
their trophic habitat from the pelagic to the nearshore zone.

* These findings suggest that P. saltatrix will not necessarily co-migrate if there is a climate-driven shift in the distribution of small pelagic fishes (their dominant prey).

* Accordingly, understanding the trophic adaptability of predators is critical for understanding their response to the impacts of climate change.


pdf available.

Reference:
Potts, W. M., R. S. J. Bealey & A.-R. Childs (2016). Assessing trophic adaptability is critical for understanding the response of predatory fishes to climate change: a case study of Pomatomus saltatrix in a global hotspot. African Journal of Marine Science, 38 (4): 539–547.

[WalkersKiller]

Very interesting Marcos.

Do you know what the status of the Chokka stocks are in SA by any chance? Normally see a lot of Chokka boats in the EC in December and havent seen any in 2 years.

[John F]

Very interesting Marcos.

Do you know what the status of the Chokka stocks are in SA by any chance? Normally see a lot of Chokka boats in the EC in December and havent seen any in 2 years.

According to a report published by the Department of Agriculture, Forestry and Fisheries (Prochazka et all., 2014 - STATUS OF THE SOUTH AFRICAN MARINE FISHERY RESOURCES 2014): "Updated analyses suggest that the squid resource is less productive than previously thought. Declines in the stock have been detected, necessitating a reduction in fishing effort."

Not sure if a new assessment has been conducted.

[REEFMAN]

Always interesting Marcos, thanks for sharing! 

[WalkersKiller]

Cool thanks Marcos, 

[John F]

Why have global shark and ray landings declined: improved management or overfishing?


* Global chondrichthyan (shark, ray, skate and chimaera) landings, reported to the United Nations Food and Agriculture Organization (FAO), peaked in 2003 and in the decade since have declined by almost 20%;

* In the FAO’s 2012 ‘State of the World’s Fisheries and Aquaculture’ report, the authors ‘hoped’ the reductions in landings were partially due to management implementation rather than population decline;

* This study tested this hypothesis;

* Post-peak chondrichthyan landings trajectories from 126 countries were modelled against seven indirect and direct fishing pressure measures and eleven measures of fisheries management performance, while accounting for ecosystem attributes;

* It was found that the recent improvement in international or national fisheries management was not yet strong enough toaccount for the recent decline in chondrichthyan landings;

* Instead, the landings declines were more closely related to fishing pressure and ecosystem attribute measures;

* Countries with the greatest declines had high human coastal population sizes or high shark and ray meat exports such as Pakistan, Sri Lanka and Thailand;

* While important progress had been made, country-level fisheries management measures did not yet have the strength or coverage to halt overfishing and avert population declines of chondrichthyans;

* Increased implementation of legally binding operational fisheries management and species-specific reporting is urgently required to avoid declines and ensure fisheries sustainability and food security.



pdf available.

Reference
Davidson, L. N. K., M. A. Krawchuk & N. K. Dulvy (2016). Why have global shark and ray landings declined: improved management or overfishing? Fish and Fisheries, 17: 438-458.

[John F]

Assessing a social norms approach for improving recreational fisheries compliance

* This study aimed to assess the suitability of the Berkowitz’ (2005) social norms approach (SNA) for improving compliance behaviour amongst recreational fishers.

* A total of 138 recreational shore anglers were interviewed in Eastern Cape, South Africa and asked about their compliance, attitudes towards compliance, perceptions of compliance and the attitudes of other anglers.

* Results indicate that angler compliance for individual regulations was relatively high (75%–90%).

* Attitudes of anglers towards compliance was positive, with >80% feeling that “breaking any regulation is wrong.”
* Yet, as predicted by the SNA, interviewees often overestimated the non- compliance and negative attitudes of other anglers, particularly as their social proximity decreased.
* Interviewees with the greatest misperceptions were also less compliant.

* The social norms present in the Eastern Cape rock and surf fishery fulfil the criteria required for the application of the SNA, suggesting that this approach may provide a suitable normative intervention for improving compliance to be used in conjunction with instrumental approaches in recreational fisheries.

PDF available.

Reference:

Bova, C. S., S. J. Halse, S. Aswani & W. M. Potts (2017). Assessing a social norms approach for improving recreational fisheries compliance. Fisheries Management and Ecology, 24: 117-125.

[John F]

Satellite snafu masked true sea-level rise for decades

http://www.nature.com/news/satellite-snafu-masked-true-sea-level-rise-for-decades-1.22312?WT.ec_id=NATURE-20170720&spMailingID=54526224&spUserID=MjA1NTA3MjA0OQS2&spJobID=1203043033&spReportId=MTIwMzA0MzAzMwS2

[colin]

  John for another  report , always interesting, 

[John F]

John for another  report , always interesting, 

Thanks. Glad somebody actually reads these

[REEFMAN]

John for another  report , always interesting, 

Thanks. Glad somebody actually reads these

Always! Love them. Very interesting.

[Marthin]

Ud be amazed how many of us read it...