Factors affecting the diel variation in commercial CPUE of Namibian hake—Can new information improve standard survey estimates?

Johnsen, Espen; Iilende, Titus

doi:10.1016/j.fishres.2007.07.013

Cited by 12 publications

(12 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The trawlers report better catches during the daytime when the fish are closer to the bottom than at night when they rise into the midwater. This corroborates findings by Johnsen and Iilende (2007) who investigated diel (24-h periodic) variation in commercial CPUE, based on logbook data. They also suggest that the vertical migration of hake and a reduced herding effect due to reduced visibility are the factors most likely impacting catchability at night.…”

Section: Vertical Migrationsupporting

confidence: 90%

“…Survey data are based on a systematic transect design, with a semirandom distribution of stations along transects and standardized effort and efficiency over time. However, these data are subject to bias due to systematic sampling errors and lack of understanding of fish behavior (Johnsen and Iilende 2007). Both survey and CPUE data are major inputs into the Namibian hake stock assessment model.…”

Section: Assessment and Management Approachesmentioning

confidence: 99%

“…Consequently, skippers are acutely aware of the movement of hake up and down the water column, and they adjust their fishing strategy accordingly, e.g., shifting to deeper water and using nets with wider openings to increase night catches. Johnsen and Iilende (2007) investigated the effect of hake behavior on commercial catches. They realized that variation observed in the CPUE cannot be taken as a direct reflection of catchability because changes in fishing strategy may be responsible for increased depth at night.…”

Section: Vertical Migrationmentioning

confidence: 99%

“…The fishers and the companies that employ them would consequently have a better understanding of how the information they provide is used. Johnsen and Iilende (2007) mention the wide range in the size of net openings employed in the Namibian demersal trawler fleet, noting the increasing use of highlift nets since 2002, but they do not seem to have access to detailed data on this or on trends over time. The suggestion that efficiency in the longline fishery may have increased by up to 25% is noteworthy because, in the assessments, fishing effort in the longline fishery is normally quantified in terms of numbers of hooks set per day, avoiding the problem of changes in the number of hooks per line.…”

Section: Different Types Of M Capensismentioning

confidence: 99%

See 3 more Smart Citations

Rebuilding the Namibian hake fishery: a case for collaboration between scientists and fishermen

Paterson¹,

Kainge²

2014

E&S

View full text Add to dashboard Cite

ABSTRACT. One of the most important fisheries in the northern Benguela is the Namibian hake fishery, which targets both Merluccius capensis and Merluccius paradoxus. In spite of attempts to rebuild the hake stocks that were severely depleted by distant-water fleets before Namibia's independence in 1990, stocks have failed to recover. Because the ecological goal of stock rebuilding competes with social and economic objectives on the political stage, the ability to make accurate abundance estimates is important. However, the precision of abundance estimates is impeded by lack of understanding of hake behavior and of the effects of environmental factors. Furthermore, at present both species of hake are assessed and managed as one Namibian stock. We present qualitative information derived from interviews that we conducted with Namibian hake trawl and longline fishers during the 2009 and 2010 fishing seasons, and information gleaned from analyzing logbook data. We contextualize both types of data within the scientific literature on Namibian hakes and the Namibian hake fishery. Fishers monitor sea surface and bottom temperature, water quality, currents, and weather, and they have detailed knowledge about the behavior and habitat of hakes. Fishers differentiate between three different types of M. capensis, which they associate with different fishing areas. They also describe innovations that have taken place over the past 20 years, which are of relevance to the assessment of fishing efficiency and effort, but have not been taken into account in the stock assessments. Our analysis of logbook data supports the increase in efficiency. The results show that closer collaboration between scientists and fishers has the potential to improve the accuracy of survey estimates and stock assessments, and thus is important for rebuilding of hake stocks and the hake fishery.

show abstract

Section: Vertical Migrationsupporting

confidence: 90%

Section: Assessment and Management Approachesmentioning

confidence: 99%

Section: Vertical Migrationmentioning

confidence: 99%

Section: Different Types Of M Capensismentioning

confidence: 99%

See 2 more Smart Citations

Rebuilding the Namibian hake fishery: a case for collaboration between scientists and fishermen

Paterson¹,

Kainge²

2014

E&S

View full text Add to dashboard Cite

show abstract

“…Furthermore, grid orientation (backwards-or forwardsleaning) and time of day (day or night) were examined to establish whether these factors have a significant influence on grid sorting. Based on previous findings, showing that behavioural differences in the aft end of a trawl can result in species-specific selectivity (Krag et al 2009) and that gadoid trawl catches vary with time of day (Michaelsen et al 1996;Johnsen and Iilende 2007), it was hypothesized that different grid orientations, in combination with distinct day and night fishing, might provide a means to optimize the sorting performance of a grid.…”

Section: Objectivesmentioning

confidence: 99%

Influence of grid orientation and time of day on grid sorting in a small-meshed trawl fishery for Norway pout (Trisopterus esmarkii)

Eigaard

Herrmann

Nielsen

2012

Aquat. Living Resour.

View full text Add to dashboard Cite

-A lightweight sorting grid was developed to reduce bycatch in the Danish small-meshed trawl fishery (22 mm full mesh in the cod end) for Norway pout in the North Sea. Experimental fishing with the grid demonstrated the possibility to capture Norway pout with only a minimum of unintended bycatch. Fishing with two different grid orientations, backwards and forwards-leaning, in distinct day and night hauls, resulted in an estimated release of between 88.4 and 100% of the total number of haddock (Melanogrammus aeglefinus) and whiting (Merlangius merlangus) entering the trawl. However, bycatch reductions were not significantly different between day and night or between grid orientations, indicating that the grid rejection of haddock and whiting is not influenced by fish behaviour. The loss of the target species, Norway pout, was low (between 5.6% and 13.7%) in comparison with the bycatch excluded, and clearly length dependent. Consequently, loss of target species would vary with the size structure of the population fished. Although results were not statistically significant, length-based analyses indicated that the grid rejection likelihood for particularly smaller Norway pout (<16 cm) was higher when fishing with the forwards-leaning grid during the night; this might be explained by behavioural and visual aspects of the fish-grid encounter process for Norway pout.

show abstract

Biology and fisheries of the shallow‐water hake ( Merluccius capensis ) and the deep‐water hake ( Merluccius paradoxus ) in Namibia

Wilhelm

Kirchner²,

Roux

et al. 2015

Hakes

View full text Add to dashboard Cite

Factors affecting the diel variation in commercial CPUE of Namibian hake—Can new information improve standard survey estimates?

Cited by 12 publications

References 23 publications

Rebuilding the Namibian hake fishery: a case for collaboration between scientists and fishermen

Rebuilding the Namibian hake fishery: a case for collaboration between scientists and fishermen

Influence of grid orientation and time of day on grid sorting in a small-meshed trawl fishery for Norway pout (Trisopterus esmarkii)

Biology and fisheries of the shallow‐water hake ( Merluccius capensis ) and the deep‐water hake ( Merluccius paradoxus ) in Namibia

Contact Info

Product

Resources

About