Shark control: experimental fishing with baited drumlines

1998 ◽  
Vol 49 (7) ◽  
pp. 653 ◽  
Author(s):  
S. F. J. Dudley ◽  
R. C. Haestier ◽  
K. R. Cox ◽  
M. Murray
Keyword(s):  
Optimal Solution ◽  
Control Programme ◽  
Shark Species ◽  
Gill Nets ◽  
Carcharhinus Leucas ◽  
Local Reduction ◽  
Shark Attacks ◽  
By Catch ◽  
Catch Rates ◽  
Physical Environmental Factors

Protective gill-nets (shark nets) have been successful in reducing the frequency of shark attacks on the coast of KwaZulu-Natal (KZN), South Africa, since 1952. This is achieved primarily through a local reduction in numbers of large sharks. Yet the nets are non-selective in terms of shark species caught and take a by-catch of dolphins, sea turtles, batoids and teleosts. Baited lines, or drumlines, as used in the Queensland shark control programme, were tested as possible alternatives to gill-nets. They demonstrated greater species selectivity for sharks and also a reduced by-catch of non-shark animals. The shark catch included the three species responsible for most shark attacks on the KZN coast, Carcharhinus leucas, Galeocerdo cuvier and Carcharodon carcharias. The probability of the bait being scavenged, or a shark being caught, was modelled in relation to a number of physical environmental factors. Although there was insufficient variability in the effort data for a quantitative comparison of catch rates between nets and drumlines, the results suggested that an optimal solution may be to deploy a combination of nets and drumlines.

scholarly journals Reducing the environmental impact of shark-control programs: a case study from KwaZulu-Natal, South Africa

2011 ◽  
Vol 62 (6) ◽  
pp. 700 ◽  
Author(s):  
Geremy Cliff ◽  
Sheldon F. J. Dudley
Keyword(s):  
South Africa ◽  
Large Scale ◽  
Shark Species ◽  
Control Programs ◽  
The Past ◽  
South Wales ◽  
Kwazulu Natal ◽  
Shark Attacks ◽  
By Catch

Large-scale shark-control programs at popular beaches in New South Wales and Queensland, Australia, and KwaZulu-Natal (KZN), South Africa, provide protection against shark attack. Although these programs have enhanced bathing safety, reducing the environmental impacts of decades of fishing for large sharks and the associated by-catch remains a challenge. Over the past three decades, there have been several interventions to reduce such impact in the KZN program. The first was the release of all live sharks, including those species known to be responsible for fatal shark attacks. Measures to reduce catches of sharks associated with the winter influx of shoals of sardines, Sardinops sagax, have been increasingly successful. In addition, extensive removal of nets has resulted in a major reduction in effort. Collectively, these initiatives reduced mortalities of sharks by 64%. Baited lines, termed drumlines, were introduced at 18 beaches, where they replaced some of the nets. The former had a far lower by-catch of rays, turtles and cetaceans and significantly lower catches of certain shark species. Replacement of some nets with drumlines is planned for the remaining beaches. Only two attacks, both non-fatal, have occurred at protected beaches in KZN over the past three decades, indicating that the program has maintained its public safety mandate while it has succeeded in reducing its impact on the environment.

Population status of 14 shark species caught in the protective gillnets off KwaZulu - Natal beaches, South Africa, 1978 - 2003

2006 ◽  
Vol 57 (2) ◽  
pp. 225 ◽  
Author(s):  
Sheldon F. J. Dudley ◽  
Colin A. Simpfendorfer
Keyword(s):  
South Africa ◽  
Potential Effect ◽  
Catch Rate ◽  
Population Increase ◽  
Shark Species ◽  
Population Status ◽  
Carcharhinus Leucas ◽  
Kwazulu Natal ◽  
Carcharhinus Obscurus ◽  
Catch Rates

Shark nets have been set off the beaches of KwaZulu–Natal, South Africa, since 1952 to reduce the risk of shark attack. The nets fish in fixed localities 400 m from shore and both directly affect local shark populations and act as fisheries-independent monitoring devices. Reliable catch information at the species level was available for the period 1978–2003. Trends in catch rate and size were used to assess the population status of 14 commonly caught shark species. In addition, a demographic modelling approach was used in conjunction with the catch information to assess the potential effect of the nets on populations. Catch rates of four species (Carcharhinus leucas, C. limbatus, Sphyrna lewini and S. mokarran) showed a significant decline, as did the mean or median length of three species (Carcharhinus amboinensis, C. limbatus and female Carcharodon carcharias). For three species that showed declining catch rates or length the potential effect of the shark nets was assessed to be low, suggesting that other sources of catch were responsible for the declining status. The potential effect of the shark nets was assessed to be high for two species (Carcharhinus obscurus and Carcharias taurus, neither of which showed declines in catch rate or length), because of very low intrinsic rates of population increase.

Fish and invertebrate by-catch in the crab pot fishery in the Isle of Man, Irish Sea

2017 ◽  
Vol 98 (8) ◽  
pp. 2099-2111
Author(s):  
Fikret Öndes ◽  
Michel J. Kaiser ◽  
Lee G. Murray
Keyword(s):  
Irish Sea ◽  
Target Species ◽  
Catch Per Unit Effort ◽  
Isle Of Man ◽  
Ecosystem Effects ◽  
By Catch ◽  
Catch Rates ◽  
Taxonomic Groups ◽  
Catch Composition ◽  
Autumn And Winter

Baited trap or pot fisheries are considered to have relatively few wider ecosystem effects on the marine environment, particularly when compared with towed mobile fishing gear. However, this assumption is rarely tested in the field. This study aimed to determine the composition of non-target species that occur in crustacean pots and to assess spatial and temporal differences in catches in the waters around the Isle of Man, Irish Sea. The data were collected using fishery independent surveys and a questionnaire study. Based on fishery independent surveys, a total of five taxonomic groups and 43 species occurred as by-catch. The dominant by-catch species was velvet crab Necora puber. The by-catch per unit effort (BPUE) for all of the non-target species was low particularly in comparison to towed bottom gear fisheries around the Isle of Man. BPUE of species composition varied considerably between different locations around the Isle of Man. The results of both the fishery independent and questionnaire data suggested that the by-catch rates varied with season with peak BPUE occurring in spring which then declined into autumn and winter. By-catch composition did not decrease significantly with an increasing target species catch. Overall, by-catch was low relative to target species catch which may be partially attributable to the use of escape panels in pot fisheries in the Isle of Man.

Schooling behaviour of jack mackerel, Trachurus declivis (Jenyns), observed in the Tasmanian purse seine fishery

1993 ◽  
Vol 44 (4) ◽  
pp. 577 ◽  
Author(s):  
H Williams ◽  
G Pullen
Keyword(s):  
School Size ◽  
East Coast ◽  
Diurnal Changes ◽  
Jack Mackerel ◽  
Schooling Behaviour ◽  
Summer Schools ◽  
By Catch ◽  
Catch Rates ◽  
Lunar Effects ◽  
Purse Seine Fishery

The seasonal, lunar and diurnal changes in schooling of jack mackerel were examined using log-book information collected from an industrial fishery off the east coast of Tasmania between 1985 and 1989. School size increased significantly from spring to autumn. The ratio between surface and subsurface schools encountered by the fishery also changed seasonally. Surface schools predominate during summer, whereas subsurface schools become more frequent during autumn. The fishery was predominantly a day fishery and no lunar effects on catch rates or fishing intensity were detected. Catches mainly comprised jack mackerel, although redbait (Emmelichthys nitidus Richardson) and blue mackerel (Scomber australasicus Cuvier) were a significant by-catch. In summer, schools were almost exclusively composed of jack mackerel, but in other seasons mixed schools were found. Data presented, together with evidence from other sources, suggest that the availability of schools to the fishery may be closely related to the availability of feed.

Postsmolt Atlantic Salmon (Salmo salar) in the Labrador Sea

1991 ◽  
Vol 48 (1) ◽  
pp. 2-6 ◽  
Author(s):  
D. G. Reddin ◽  
P. B. Short
Keyword(s):  
Atlantic Salmon ◽  
Salmo Salar ◽  
Age Distribution ◽  
Labrador Sea ◽  
Scale Reading ◽  
Gill Nets ◽  
Atlantic Salmon Salmo Salar ◽  
Catch Rates ◽  
Abundance And Distribution ◽  
High Catch

In order to learn more about the existence, abundance, and distribution of postsmolt Atlantic salmon (Salmo salar) in the Labrador Sea, exploratory fishing was done with surface-set gill nets in early autumn of 1987 and 1988. In total, there were 468 salmon of various sea ages captured, of which 207 were postsmolts. The high catch rates compared with catch rates from Greenland suggest that the population of postsmolts in the Labrador Sea may be large. Postsmolts from rivers in Maine to Labrador were caught in the Labrador Sea, as indicated by Carlin tags and river age distribution from scale reading. The highest catch rates of postsmolts occurred in the Labrador Sea between 56° and 58°N latitude.

Mitigation of harbour porpoise (Phocoena phocoena) by-catch in the gillnet fishery in the lower Bay of Fundy

1999 ◽  
Vol 56 (1) ◽  
pp. 113-123 ◽  
Author(s):  
Edward A Trippel ◽  
Michael B Strong ◽  
John M Terhune ◽  
Jeremy D Conway
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Field Testing ◽  
Harbour Porpoise ◽  
Clupea Harengus ◽  
Bay Of Fundy ◽  
Phocoena Phocoena ◽  
By Catch ◽  
Catch Rates ◽  
Wind Sea

Demersal gill nets equipped with acoustic alarms reduced harbour porpoise (Phocoena phocoena) by-catch rates by 77% over those without alarms in the Swallowtail area of the lower Bay of Fundy during field testing in August 1996 (68% reduction) and 1997 (85% reduction) (both years combined, three harbour porpoises in 249 alarmed nets versus 14 harbour porpoises in 267 nonalarmed nets). The alarms spaced 100 m apart along the net floatline produced a 0.3-s pulse at 10-12 kHz every 4 s at a level of 133-145 dB re 1 µPa at 1 m. In conditions of no rain and low wind (Sea State 0-2) the alarms were presumed to be clearly audible to harbour porpoises at ranges of 0.1-0.6 km. Catch rates of Atlantic herring (Clupea harengus), Atlantic cod (Gadus morhua), and pollock (Pollachius virens) were not significantly different in alarmed and nonalarmed nets (except in one season when pollock were caught in lower numbers in alarmed nets). Harbour porpoise by-catch and herring movements may be linked. During years of low herring abundance, we also observed low harbour porpoise entanglement rates.

Use of Oceanographic Forecasts and Echosounders to Guide and Enhance an Inshore Gillnet Fishery for Atlantic Cod (Gadus morhua)

1993 ◽  
Vol 50 (10) ◽  
pp. 2129-2136 ◽  
Author(s):  
G. A. Rose ◽  
W.C. Leggett
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Fishing Effort ◽  
Shallow Waters ◽  
Gill Nets ◽  
Rule Of Thumb ◽  
Combined Use ◽  
Catch Rates ◽  
Depth Ranges ◽  
High Fish

Vessels fishing with gill nets for Atlantic cod (Gadus morhua) in the northern Gulf of St. Lawrence in 1985 and 1986 concentrated their fishing effort in shallow waters (<50 m) where cod densities were highest (to 0.5/m3). In both years, seasonal trends (June–August) in mean daily deployment depths of gill nets were positively correlated with mean depths at which cod were surveyed (1985, r = 0.71; 1986, r = 0.51, Ps < 0.05). Daily catch rate variability of individual vessels was accounted for by fish "flux" adjacent to nets (44%), vessel operator skill (19%), and "flux"–skill interaction (8%; total R2 = 0.71). A guided vessel directed to fish at sites predicted to have high fish flux (located down-current from high-density cod aggregations identified by echosounding within depth ranges forecast to be favorable to cod by "rule of thumb" wind-based oceanographic models) had higher catch rates (mean 1.3 t/d) than the fleet average and its own average fishing without guidance (means 0.4 t/d, P's < 0.05). Directed searches were of shorter duration (mean 0.5 h) than searches conducted at random (1.5 h). Combined use of echosounders and air–sea-based forecasts of cod distribution could help stabilize catch rates, especially at times of poor fish availability inshore.

scholarly journals Trends in Stranding and By-Catch Rates of Gray and Harbor Seals along the Northeastern Coast of the United States: Evidence of Divergence in the Abundance of Two Sympatric Phocid Species?

PLoS ONE ◽  
2015 ◽  
Vol 10 (7) ◽  
pp. e0131660 ◽  
Author(s):  
David W. Johnston ◽  
Jaime Frungillo ◽  
Ainsley Smith ◽  
Katie Moore ◽  
Brian Sharp ◽  
...  
Keyword(s):  
United States ◽  
The United States ◽  
Harbor Seals ◽  
By Catch ◽  
Catch Rates ◽  
Northeastern Coast

Response of barramundi, Lates calcarifer, populations in the Fly River, Papua New Guinea to mining, fishing and climate-related perturbation

2005 ◽  
Vol 56 (7) ◽  
pp. 969 ◽  
Author(s):  
David Milton ◽  
Markson Yarrao ◽  
Gary Fry ◽  
Charles Tenakanai
Keyword(s):  
Papua New Guinea ◽  
Negative Impact ◽  
New Guinea ◽  
Commercial Fishery ◽  
Artisanal Fishery ◽  
Lates Calcarifer ◽  
Gill Nets ◽  
Breeding Grounds ◽  
Catch Rates ◽  
Fly River

Migrating barramundi (Perciformes : Centropomidae) spawners support a valuable artisanal fishery on the coast of south-western Papua New Guinea. This fishery declined dramatically during the 1990s shortly after the large Ok Tedi copper mine began in the headwaters of the large Fly River nearby. In order to understand the factors causing the decline, populations were sampled quarterly with gill-nets at over 20 sites throughout the Fly River from 1987 to 2001. Barramundi were most abundant in the middle and upper reaches of the Fly River. No evidence was found that output from the large Ok Tedi mine was negatively impacting on barramundi catch rates. However, the commercial fishery in the middle Fly River was found to have a negative impact on the weight of barramundi in monitoring catches in that region. Additionally, catch rates of juvenile barramundi (1 year olds) in the Fly River were negatively correlated with the amount of rainfall on the breeding grounds during the previous monsoon. This suggests that the reduced catch rates in the coastal commercial fishery in the late 1980s and early 1990s may have been affected by both the riverine commercial fishery and the El Niño (ENSO) that occurred at that time.

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