Science corner: latest fish & fisheries research

[REEFMAN]

Very interesting John F! Keep them coming! 

[John F]

Reefz, at this stage I think it is actually scary! The latest IPCC report draws a bleak picture in terms of climate change for the next 100 years. I'm afraid our children and grand-children will inherit a pretty messed-up planet! 

[John F]

Socio-economic aspects of the Sodwana Bay SCUBA diving industry, with a specific focus on sharks

* Understanding socio-economic aspects of the diving industry at Sodwana Bay, including data on participant motivation and expenditure, is crucial for the effective management of the St Lucia and Maputaland marine protected areas, South Africa.

* Between July 2011 and July 2012 a total of 59 553 dives was conducted by 15 780 divers.

* Data were collected by means of the administration of a semi-structured survey questionnaire to 750 dive participants.

* Participant responses indicated that the direct value of diving to the iSimangaliso Wetland Park was R75 484 784.

* The majority of dives at Sodwana were on coral-covered sandstone reefs (95.2%), with shark diving accounting for only 4.8% of dives.

* Although sharks were not the primary attraction for divers to visit Sodwana, 84.2% of respondents stated that they were interested in shark diving and that more opportunities to dive with sharks would encourage them to revisit Sodwana more often.

* Attaching an economic value to sharks as a dive attraction to Sodwana and highlighting their potential for the growth of the dive industry may act as leverage for their protection against fishing within iSimangaliso.


pdf available.

Reference:
Dicken, M. L. (2014). Socio-economic aspects of the Sodwana Bay SCUBA diving industry, with a specific focus on sharks. African Journal of Marine Science, 36: 39-47.

[John F]

Selective exploitation of fish populations by recreational anglers may lead to evolutionary downsizing of adults

* When gene flow is limited and harvesting is intensive, fishing may alter life histories and favour trait combinations that collectively reduce adult body size;

* However, empirical evidence of downsizing of adults in small-bodied coastal fish is still scarce, in part due to the lack of knowledge about the selective nature of certain fishing gears, such as recreational angling, and the difficulties in estimating the dispersion of pelagic early-life stages;

* Using the small-bodied sedentary coastal marine fish Serranus scriba as a model, it is empirically shown that:

* Recreational angling selects for life-history traits (i.e. increased reproductive investment) that promote downsizing of adults;

* Second, using Lagrangian particle dispersion modelling, we show how local hydrodynamics generates patterns of limited connectivity and the emergence of meta-population structure;

* Finally, the life histories presently observed in isolated populations of S. scriba that experienced differential fishing pressure matched expectations of fishing-induced downsizing of adult body size.

* Body size is an important trait in aquatic food webs, and evolutionary downsizing might have unforeseen consequences.

* From a precautionary perspective, maintaining the metapopulation structure and the full range of genotypes inherent in them is important, even for small-bodied, geographically restricted fish species that are mainly harvested by recreational anglers.


PDF available.

Reference:
Alós, J., M. Palmer, I. A. Catalan, A. Alonso-Fernández, G. Basterretxea, A. Jordi, L. Buttay, B. Morales-Nin & R. Arlinghaus
(2014). Selective exploitation of spatially structured coastal fish populations by recreational anglers may lead to evolutionary downsizing of adults. Marine Ecology Progress Series, 503: 219-233.

[icstuff]

Thank you John, I remember reading somewhere that size restrictions on commercial species caused them to spawn at a younger age/size. Will look for the study but I cant remember where I saw it.

[REEFMAN]

75 million on diving alone in one year at Sodwana!!    Serious industry that!

[icstuff]

Google never forgets:
http://www.nature.com/news/ocean-conservation-a-big-fight-over-little-fish-1.12325

[John F]

Thank you John, I remember reading somewhere that size restrictions on commercial species caused them to spawn at a younger age/size. Will look for the study but I cant remember where I saw it.

Yeap... classical signs of overfishing...

i) decrease in CPUE
ii) decrease in average size of the fish
iii) shift in the catch composition
iv) fish start reproducing at younger age/size
v) fishery collapse

[Krystyna]

Just reading through from the beginning of the thread here  and one cannot help but thinking that we know so little of what is really happening in our oceans and what the future holds for us  recreational fisherman.
 I unfortunately disagree with much of what may be regarded as factual evidence and what is mere speculation on the part of scientists and researchers ,  regarding many specific case  studies and the resultant methods that are employed to conserve species


 What is most evident  is that so much more research is required , and it is only through the combined efforts of every person who has any involvement with taking anything from our oceans (and this includes the final consumers (which includes 'chickens'  ) to wake up to the realities  that fish  stocks are dwindling at an alarming rates world wide.
 Although the impact of recreational fishermen cannot summarily be discarded in contributing to this   , in my opinion , governmental regulations, as far as commercial fisheries , has by  far the greatest effect on the overall picture , that we , the recreational fishermen , will ever contribute to these unfortunate statistics. 
At the end of the day , for me everything relates back to wise and sustainable ecosystem management , and here governments in my opinion ,  are failing dismally- the underlying factors for this is to much   and  far to little contributions from their side in the way of resources and money  allocated to get more research underway...get this right , then there is possibly a future for us to continue doing what we enjoy

[John F]

Response of fish communities to the deployment of estuarine artificial reefs for fisheries enhancement

* Artificial reef systems constructed in three south-eastern Australian estuaries were monitored over a four-year period;

* Recruitment of fish to the artificial reefs was rapid, with significantly greater species richness observed on artificial reefs than on natural habitats for the majority of locations and times;

* The rate of community change varied between estuaries and appeared to be related to the quality and amount of existing habitat and the distance of the artificial reef from sources of recruitment;

* General patterns were also identified among estuaries driven by strong recruitment, followed by a rapid reduction in several mobile schooling species.

* By contrast, there was early and sustained recruitment of a variety of sparid species, which are of importance to recreational and commercial fisheries.


PDF available.

Reference:
Lowry, M. B., T. M. Glasby, C. A. Boys, H. Folpp, I. Suthers & M. Gregson (2014). Response of fish communities to the deployment of estuarine artificial reefs for fisheries enhancement. Fisheries Management and Ecology, 31: 42-56.

[John F]

Thirty years of monitoring traditional fish trap catches at Kosi Bay, KwaZulu-Natal, South Africa, and management implications

* The catches of the traditional fish traps in the Kosi Bay estuarine lakes were monitored over a 30-year period from 1981 to 2010;

* Monitoring data were used to provide estimates of, and insights into, catch size and species composition as well as seasonal and annual cycles of catch abundance;

* Over 1.2 million fish, comprising 43 species and 23 families, were estimated to have been caught during the study period.

* Tag-and-release data were used to estimate the impact of trap fishing on fish stocks and comparisons were made with recreational fishing to indicate overall fishing pressure and the sustainability of the fishing;

* Trap numbers remained fairly similar from the first year of monitoring (1981) until 1994, but thereafter they more than trebled by 2001; although numbers decreased after this, they remained well above earlier levels;

* During this period, recreational angling was an important factor, and gillnetting - both legal and illegal - added to the fishing pressure;

* Information from the fish trap monitoring, together with results from fish mark and recapture studies, suggest a very high, and possibly unsustainable, catch rate that requires management intervention to return them back to historical and sustainable levels.


PDF available.

Reference:

Kyle, R. (2013). Thirty years of monitoring traditional fish trap catches at Kosi Bay, KwaZulu-Natal, South Africa, and management implications. African Journal of Marine Science, 35: 67-78.

[icstuff]

30 years study! but will anyone take action or will we need further study ...

[John F]

30 years study! but will anyone take action or will we need further study ...

  The info to support management is there... 

[colin]

We have caught very few fish on our last trips to Kosi. With 3 boats and 9 anglers we did little better than put fish on the table for meals . The gillies saw '' fishermen'' on boats buying rock salmon from the traps . IMO many traps are used to keep the fish alive/fresh until bakkies arrive to buy and transport the fish caught in the gill nets'  I was was told that the nets are are up to 300m in length . We saw the bakkies on most days, parked under trees next to the traps on 2nd lake, The gillies say this is normal practice.

[WalkersKiller]

Marcos please could you mail me that pdf 

[John F]

Assessment of the Trachinotus botla shore-fishery in KwaZulu-Natal, South Africa

* The shore-fishery for Trachinotus botla in KwaZulu-Natal appears to be in a stable state.

* A per-recruit assessment showed that the species is currently underexploited (spawner biomass-per-recruit = 75% of pristine levels) and that fishing mortality could theoretically be increased.

* The fishery was shown to display considerable spatial and temporal variability with resource abundance increasing north-easterly towards Mozambique with catch per unit effort (CPUE) peaking during summer.

* Trachinotus botla displayed random movement patterns indicative of a surf-zone resident, with 78% of the recaptures being made within 1 km of the tagging site.

* The movement pattern observed was not affected by fish size or time at liberty.

* An increasing trend in mean annual CPUE since 2002 suggests that either the resource is increasing since the promulgation of the ban on beach driving or possibly as a result of increased targeting of this species using a relatively modern technique known locally as ‘dropshot’ fishing.

* It is likely that the beach driving ban has shifted fishing effort to accessible nodes along the coast where there is some evidence of localised overexploitation.


PDF available.

Reference:
Parker, D., A. J. Booth & B. Q. Mann (2013). A spatio-temporal assessment of the Trachinotus botla shore-fishery in KwaZulu-Natal, South Africa. African Journal of Marine Science, 35: 35-46.

[John F]

Using posts to an online social network to assess fishing effort

* Fisheries management has evolved from reservoir to watershed management, creating a need to simultaneously
gather information within and across interacting reservoirs.

* However, costs to gather information on the fishing effort on multiple reservoirs using traditional creel methodology are often prohibitive.

* Angler posts about reservoirs online provide a unique medium to test hypotheses on the distribution of fishing pressure.

* It is shown that the activity on an online fishing social network is related to fishing effort and can be used to facilitate management goals.

* The Nebraska Fish and Game Association Fishing Forum was searched for all references from April 2009 to December 2010 to 19 reservoirs that comprise the Salt Valley regional fishery in southeastern Nebraska.

* The number of posts was positively related to monthly fishing effort on a regional scale, with individual reservoirs having the most annual posts also having the most annual fishing effort.

* Furthermore, this relationship held temporally. Online fishing social networks provide the potential to assess effort on larger spatial scales than currently feasible.

pdf available.


Reference:

Martin, D. R., C. J. Chizinski, K. M. Eskridge & K. L. Pope (2014). Using posts to an online social network to assess fishing effort. Fisheries Research, 157: 24-27.

[John F]

Residency Patterns and Migration Dynamics of Adult Bull Sharks  on the East Coast of Southern Africa

* Bull sharks (Carcharhinus leucas) are globally distributed top predators that play an important ecological role within coastal marine communities;

* However, little is known about the spatial and temporal scales of their habitat use and associated ecological role;

* In this study, passive acoustic telemetry was employed to investigate the residency patterns and migration dynamics of 18 adult bull sharks (195–283 cm total length) tagged in southern Mozambique for a period of between 10 and 22 months;

* The majority of sharks (n = 16) exhibited temporally and spatially variable residency patterns interspersed with migration events;

* Ten individuals undertook coastal migrations that ranged between 433 and 709 km (mean = 533 km) with eight of these sharks returning to the study site;

* During migration, individuals exhibited rates of movement between 2 and 59 km.d21 (mean = 17.58 km.d21) and were recorded travelling annual distances of between 450 and 3760 km (mean = 1163 km);

* Migration towards lower latitudes primarily took place in austral spring and winter and there was a significant negative correlation between residency and mean monthly sea temperature at the study site;

* This suggested that seasonal change is the primary driver behind migration events but further investigation is required to assess how foraging and reproductive activity may influence residency patterns and migration;

* Results from this study highlight the need for further understanding of bull shark migration dynamics and suggest that effective conservation strategies for this vulnerable species necessitate the incorporation of congruent trans-boundary policies over large spatial scales.

PDF available.

Reference:
Daly, R., M. J. Smale, P. D. Cowley & P. W. Froneman (2014). Residency patterns and migration dynamics of adult bull sharks (Carcharhinus leucas) on the East coast of southern Africa. PLoS ONE, 9(10): e109357.

[John F]

    Seagrasses in the age of sea turtle conservation and shark  overfishing
 
* Efforts to conserve globally declining herbivorous green sea turtles   have resulted in promising growth of some populations.

* These trends   could significantly impact critical ecosystem services provided by   seagrass meadows on which turtles feed.

* Expanding turtle populations   could improve seagrass ecosystem health by removing seagrass biomass and   preventing of the formation of sediment anoxia.

* However, overfishing of   large sharks, the primary green turtle predators, could facilitate   turtle populations growing beyond historical sizes and trigger   detrimental ecosystem impacts mirroring those on land when top predators   were extirpated.

* Experimental data from multiple ocean basins suggest   that increasing turtle populations can negatively impact seagrasses,   including triggering virtual ecosystem collapse.

* Impacts of large turtle   populations on seagrasses are reduced in the presence of intact shark   populations.

* Healthy populations of sharks and turtles, therefore, are   likely vital to restoring or maintaining seagrass ecosystem structure,   function, and their value in supporting fisheries and as a carbon sink.


PDF available.

Reference Type: Journal Article
Heithaus, M. R., T. Alcoverro, R. Arthur, D. A. Burkholder, K. A. Coates, M. J. A. Christianen, N. Kelkar, S. A. Manuel, A. J. Wirsing, W. J. Kenworthy & J. W. Fourqurean (2014). Seagrasses in the age of sea turtle conservation and shark overfishing. Frontiers in Marine Science, 1: 6 pp.

[John F]

Catch rates and income are associated with fisheries management restrictions and not an environmental disturbance, in a heavily exploited tropical fishery

* The influence of the largest temperature anomaly in recent history, the 1997-1998 El Niño-Indian Ocean Dipole anomaly that killed half of the corals in the Indian Ocean, with a nearly coincident increase in fisheries management restrictions on coral reef fisheries in southern Kenya was evaluated and compared;

* Seawater temperatures, benthic primary producers, and fishing effort and catch rate and income time series collected over the 1993-2012 period were evaluated using time series and variable cointegration methods;

* An observed decline and subsequent increase in catch rates was closely associated with the implementation of increasing fisheries restrictions and was not predictably cointegrated with the temperature or the primary producer’s time series;

* This may have occurred because the disturbance was pulsed with a limited 6 yr impact on the primary producers and the fishery was heavily utilized and composed of fast-growing generalist species with broad diet and habitat needs

* Consequently, under these conditions, promoting fisheries restrictions is expected to attenuate the predicted declines in fish catches projected by global warming.


PDF available.

Reference
McClanahan, T. R. & C. A. Abunge (2014). Catch rates and income are associated with fisheries management restrictions and not an environmental disturbance, in a heavily exploited tropical fishery. Marine Ecology Progress Series, 513: 201-213.