Effects of underestimating catch and effort on surplus production models

Omori, Kristen L.; Hoenig, John M.; Luehring, Mark A.; Baier-Lockhart, Kathy

doi:10.1016/j.fishres.2016.05.021

Cited by 23 publications

(11 citation statements)

References 23 publications

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“…There was a much higher risk to long‐term yields and stock biomass when specifying positively biased natural mortality rates, recruitment compensation and catch levels than the equivalent negative bias. Qualitatively, the direction of risk derived from closed‐loop simulation in these analyses correspond with sensitivities reported by previous research investigating age‐structure model estimates to varying natural mortality rates (Clark, ; Deroba & Schueller, ; Williams, ) and catch biases (Van Beveren et al, ; Omori, Hoenig, Luehring, & Baier‐Lockhart, ; Rudd & Branch, ). Additionally, this analysis demonstrates that reconstructing historical catches to account for under‐reporting (e.g.…”

Section: Discussionsupporting

confidence: 84%

Misspecification in stock assessments: Common uncertainties and asymmetric risks

2019

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Common uncertainties in stock assessment relate to parameters or assumptions that strongly determine both the estimates of quantities of management interest (e.g. stock depletion) and related reference points (e.g. biomass at maximum sustainable yield). The risks associated with these uncertainties are often presented to managers in the form of decision tables. However, a formal evaluation of the risks from misspecifying an assessment model over time‐horizons spanning multiple assessment cycles requires closed‐loop simulation. There were two aims of this study: (a) develop an approach to identify and evaluate asymmetries in risk to yields and spawning biomass due to biases in key parameters and data sources in a stock assessment model, (b) quantify the relative importance of correctly specifying the various assessment attributes. A computationally efficient stock reduction analysis was evaluated using closed‐loop simulation to identify risks associated with a stock assessment with persistent positive and negative biases in the key parameters and inaccurate assumptions regarding data sources. Six types of assessment misspecification were examined, namely the assumed natural mortality rate, the assumed recruitment compensation ratio, the assumed age of maturity, a hyper‐stable or hyper‐deplete index of abundance, over‐ or under‐reporting of historical catch, and misspecification of the assumed shape of the selectivity curve. This study reveals large asymmetries in risk associated with common uncertainties in stock assessment processes. We highlight the value of reproducible and computationally efficient stock assessment models that can be investigated by closed‐loop simulation before being used for fisheries management.

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Section: Discussionsupporting

confidence: 84%

Misspecification in stock assessments: Common uncertainties and asymmetric risks

2019

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“…Penentuan ini didasarkan pada analisis data produksi surplus, yaitu dari data hasil tangkapan (catch) dan jumlah upaya penangkapan (effort) dalam kurun waktu 10 tahun. Perikanan dapat dikelola berdasarkan model produksi surplus bila tersedia data hasil tangkapan atau catch dan jumlah upaya penangkapan atau effort (Omori et al 2016).…”

Section: Pendahuluanunclassified

Pendugaan Status Sumberdaya Perikanan Skala Kecil di Kota Semarang

Kristiana¹,

Malik²,

Anwar³

2021

JPPT

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Perikanan di Kota Semarang didominasi oleh perikanan skala kecil. Hal ini ditandai dengan penggunaan armada perikanan paling besar 10 gros ton yang beroperasi di dekat pantai. Data statistik perikanan selama 10 tahun (2010-2019) terlihat hasil tangkapan yang mulai menurun, sementara perkembangan jumlah unit penangkapan yang semakin meningkat. Hal ini mengindikasikan stok ikan mulai berkurang dan tingkat pemanfaatan sumberdaya perikanan mengarah overfishing. Hal tersebut diperkuat dengan hasil pengamatan langsung di lapangan yang menunjukkan jumlah hasil tangkapan cenderung sedikit dan ukuran ikan yang tertangkap cenderung kecil. Tujuan penelitian ini adalah menganalisis status sumberdaya perikanan skala kecil di Kota Semarang. Metode yang dipakai dalam penelitian ini adalah analisis data runtun waktu (time series) produksi surplus yaitu data dari hasil tangkapan (ton/tahun) dan jumlah alat tangkap (unit), dalam kurun waktu 10 tahun (2010-2019), untuk menghitung nilai catch per-unit effort (CPUE), potensi maksimum lestari (MSY), jumlah effort optimum (fopt), tingkat pemanfaatan (TP) dan tingkat kapasitas (TK). Penelitian ini diperoleh hasil adanya tren penurunan CPUE; hasil tangkapan/produksi perikanan eksisting tahun 2019 telah melewati nilai MSY-nya yaitu sebesar 479 ton/tahun (Schaefer) dan 439,11 ton/tahun (Fox); tingkat pemanfaatan lebih dari 100% yaitu sebesar 108-127% (Schaefer) dan 118-138% (Fox), sehingga perikanan skala kecil di Kota Semarang berada pada tingkat over-exploited. Berdasarkan analisis fopt menunjukkan jumlah alat tangkap yang digunakan (fexisting) telah melebihi jumlah optimumnya dengan tingkat kapasitas penangkapan melebihi 100%, sehingga perikanan skala kecil di Kota Semarang telah mengalami kelebihan kapasitas penangkapan (overcapacity).

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“…In addition to the challenges of monitoring legal activities, unreported and unregulated fishing presents an additional significant challenge to informing stock assessments (Cawthorn & Mariani, 2017). For example, unreported catches and effort can lead to severely biased estimates of biomass and other model outputs (Omori et al, 2016). This creates a mixed situation of partial coverage in data streams resulting in uncertainty that deserves respect and acknowledgement, but such uncertainty is an insufficient reason to avoid using science to inform management (Dowling et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Stock assessment on fishery‐dependent data: Effect of data quality and parametrisation for a red snapper fishery

Tagliarolo

Cope

Blanchard

2021

Fisheries Management Eco

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Data availability, and unreported and unregulated fishing are significant obstacles to evaluating stock status, especially in tropical areas. Limitations in data quantity and quality can lead to model misspecification and erroneous data treatments, potentially causing important changes in model outputs and subsequent management implications. Red snapper Lutjanus purpureus (Poey) in French Guiana provides an example of a stock with a long-time series of fishery-dependent data subject to large uncertainty.A flexible catch-at-age model (Stock Synthesis) was applied to the available data and compared to an historically applied assessment approach. Inter-model variability based on different model specifications and data treatments were compared to identify better the status of the resource. Results showed that a major source of uncertainty in the model was the inclusion of a catch-per-unit-effort abundance index with questionable ability to track abundance. The Stock Synthesis model provided a more flexible and viable method than the virtual population analysis approach. Despite large uncertainty, models depicted a similar trend with a notable stock depletion in the late 1990s but with two distinct biomass trends in more recent years depending on the treatment. To reduce uncertainty and preserve this important economic resource, new data collection programmes and management policies are needed.

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Effects of underestimating catch and effort on surplus production models

Cited by 23 publications

References 23 publications

Misspecification in stock assessments: Common uncertainties and asymmetric risks

Misspecification in stock assessments: Common uncertainties and asymmetric risks

Pendugaan Status Sumberdaya Perikanan Skala Kecil di Kota Semarang

Stock assessment on fishery‐dependent data: Effect of data quality and parametrisation for a red snapper fishery

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