Estimation of Unreported Catch in a Commercial Trawl Fishery

McBride, Margaret Mary

doi:10.2960/j.v18.a2

Cited by 5 publications

(5 citation statements)

References 2 publications

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“…Second, earlier models of highgrading assumed linear discarding costs: this has led to corner solutions where either all or none of each grade of fish is discarded. 1 The presence of these corner solutions contrasts with empirical evidence from several fisheries where discarding has been banned (McBride and Fotland 1996;Palsson, Schopka, and Einarsson 2003). In these fisheries, fishers typically choose internal solutions, with some, but not total, discarding of the lower grades of fish.…”

mentioning

confidence: 78%

Highgrading in Quota‐Regulated Fisheries: Evidence from the Icelandic Cod Fishery

Kristófersson

Rickertsen

2009

American J Agri Economics

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A model with nonlinear discarding costs is developed for a fishery with an individual transferable quota (ITQ) program. The model shows that limited hold capacity and ITQs provide incentives to discard fish. The model is applied to the Icelandic ITQ-regulated cod fishery to test for highgrading and to predict the discarded quantities of different grades of fish. The results indicate that vessels are involved in highgrading, but there is no evidence of quota price-induced highgrading. The predicted total discarded quantities are 4.7% and 2.7% of total landings for gillnet and longline vessels, respectively. These correspond well with official biometric estimates.

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confidence: 78%

Highgrading in Quota‐Regulated Fisheries: Evidence from the Icelandic Cod Fishery

Kristófersson

Rickertsen

2009

American J Agri Economics

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“…Earlier estimates of discards in Norwegian fisheries (McBride and Fotland, 1996;Dingsør, 2001;Valdemarsen and Nakken, 2002;Nedreaas et al, 2015) were based on inference or assumptions due to a lack of direct scientific sampling of discards. Berg and Nedreaas (2020) presented a generalized approach to estimating discards in the coastal gillnet fisheries using direct observations by the Norwegian Reference Fleet.…”

Section: Discussionmentioning

confidence: 99%

Discards of cod (Gadus morhua) in the Norwegian coastal fisheries: improving past and future estimates

Berg

Clegg

Blom

et al. 2022

ICES Journal of Marine Science

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Discarding can be an unknown source of biases and uncertainties in stock assessments. Discarding patterns and quantities vary so a routine methodology for estimating discards is important to give a better picture of total catches, and potentially mortality, in fisheries. Using data from the Norwegian Reference Fleet between 2012 and 2018, this study presents a revised methodology for estimating discards of cod (Gadus morhua) in the Norwegian coastal gillnet fisheries, which accounts for variations in discarding between vessels and uncertainties in the conversion of numbers to weight discarded. The estimated average discard rate of cod (weight of cod discarded as percentage of total weight caught) is 0.55% (95% confidence interval: 0.45–0.70%), although discard rates in southern areas were an order of magnitude higher than in northern areas. We also present an exploratory analysis of the drivers behind discarding using a random forest regression model. Spatial variations and fishing intensity were identified as the most important drivers of discarding. Results from this study suggest ways in which self-sampled data can be used to estimate discards in Norwegian coastal fisheries, and where the accuracy of future estimates can be improved when a higher resolution data collection programme is established.

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“…Opportunities can arise where specific survey gear has been calibrated against commercial gear in the fishery, allowing for appropriate conversions (e.g. Mayo et al 1981;Hylen and Jacobsen 1987;McBride and Fotland 1996;Dingsør 2001b). However, routine estimations would require regular calibration studies to reflect developments in gear technology and fishing patterns by the commercial fleet.…”

Section: Scientific Surveysmentioning

confidence: 99%

“…Updating calibrations is not sustainable in the long-term for regular estimates of unreported catches, especially as modern fishing technology rapidly develops. Therefore, studies that have used this approach have acknowledged it is only useful in the absence of direct observations of fishing activity (McBride and Fotland 1996).…”

Section: Scientific Surveysmentioning

confidence: 99%

“…Other estimates of discards and unreported catches in Norway (Dingsør 2001a;Valdemarsen and Nakken 2002) indicate low levels of discarding relative to the global average (Pérez Roda et al 2019), whilst numerous studies have provided snapshot estimates for individual fisheries (e.g. Hylen and Jacobsen 1987;McBride and Fotland 1996;Dingsør 2001b;Breivik et al 2017). The available estimates, both nationally and for individual fisheries, have been constrained by a lack of at-sea observations throughout time, focussing on shorter timescales and specific fisheries where data are available.…”

Section: Introductionmentioning

confidence: 99%

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Applying global best practices for estimating unreported catches in Norwegian fisheries under a discard ban

Clegg

Kennelly

Blom

et al. 2020

Rev Fish Biol Fisheries

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In addition to their role as a fisheries management tool, discard bans can be effective in improving knowledge of total catches via the requirement to land and report all catches. This shifts the focus to understanding the scale of unreported catches in fisheries, rather than only on discards. However, the presence of a discard ban can cause problems with estimation process, as it involves the observation of illegal activities, and the complex sources of unreported catches require a different approach to estimation. The Norwegian discard ban was introduced in 1987 as part of a wider suite of regulatory measures to improve exploitation patterns in commercial fisheries, but a framework for the regular estimation of unreported catches has yet to be established and operationalised. Here, we aim to identify global best practices for estimating unreported catches under a discard ban and assess their applicability to Norwegian fisheries. We approach this in three steps: (1) defining the scope of an estimation, (2) data collection, and (3) the actual procedure for estimation. We discuss how each step can affect the quality of an estimate with regards to accuracy, precision, practical limitations and whether the estimate is fit for purpose. Finally, we provide a list of recommendations for future studies and identify key knowledge gaps and limitations regarding their application to Norwegian fisheries.

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Estimation of Unreported Catch in a Commercial Trawl Fishery

Cited by 5 publications

References 2 publications

Highgrading in Quota‐Regulated Fisheries: Evidence from the Icelandic Cod Fishery

Highgrading in Quota‐Regulated Fisheries: Evidence from the Icelandic Cod Fishery

Discards of cod (Gadus morhua) in the Norwegian coastal fisheries: improving past and future estimates

Applying global best practices for estimating unreported catches in Norwegian fisheries under a discard ban

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