Models of Tag Dynamics with Exchange between Available and Unavailable Populations

1989 ◽  
Vol 46 (8) ◽  
pp. 1356-1366 ◽  
Author(s):  
Ray Hilborn
Keyword(s):  
Loss Rate ◽  
Fishing Effort ◽  
Estimation Methods ◽  
Fishing Gear ◽  
Natural Mortality ◽  
Time Varying ◽  
Skipjack Tuna ◽  
Fishing Mortality ◽  
Release Group ◽  
Parameter Estimation Methods

Four models of the dynamics of an exploited population of fish are presented, and methods for the estimation of the parameters of each model from a mark recapture experiment are developed. The four models are (1) constant loss rate from the population, (2) constant natural mortality, with time varying fishing mortality proportional to fishing effort, (3) constant natural mortality, and time varying vulnerability to fishing gear, and (4) interchange between a vulnerable population and an invulnerable one, with natural mortality occurring in both populations, but fishing mortality occurring only in one. The parameter estimation methods are developed for a single release group recovered over discrete intervals. Each of these models is applied to tagging data on skipjack tuna (Euthynnus pelamis) in the western tropical Pacific.

Detecting mortality variation to enhance forage fish population assessments

2018 ◽  
Vol 76 (1) ◽  
pp. 124-135 ◽  
Author(s):  
Nis S Jacobsen ◽  
James T Thorson ◽  
Timothy E Essington
Keyword(s):  
Test Performance ◽  
Size Structure ◽  
Stock Assessment ◽  
Reference Points ◽  
Forage Fish ◽  
Natural Mortality ◽  
Time Varying ◽  
Fishing Mortality ◽  
Catch Data ◽  
Over Time

Abstract Contemporary stock assessment models used by fisheries management often assume that natural mortality rates are constant over time for exploited fish stocks. This assumption results in biased estimates of fishing mortality and reference points when mortality changes over time. However, it is difficult to distinguish changes in natural mortality from changes in fishing mortality, selectivity, and recruitment. Because changes in size structure can be indicate changes in mortality, one potential solution is to use population size-structure and fisheries catch data to simultaneously estimate time-varying natural and fishing mortality. Here we test that hypothesis, using a simulation experiment to test performance for four alternative estimation models that estimate natural and fishing mortality from size structure and catch data. We show that it is possible to estimate time-varying natural mortality in a size-based model, even when fishing mortality, recruitment, and selectivity are changing over time. Finally, we apply the model to North Sea sprat, and show that estimates of recruitment and natural mortality are similar to estimates from an alternative multispecies population model fitted to additional data sources. We recommend exploring potential trends in natural mortality in forage fish assessments using tools such as the one presented here.

scholarly journals Time-varying natural mortality in fisheries stock assessment models: identifying a default approach

2014 ◽  
Vol 72 (1) ◽  
pp. 137-150 ◽  
Author(s):  
Kelli F. Johnson ◽  
Cole C. Monnahan ◽  
Carey R. McGilliard ◽  
Katyana A. Vert-pre ◽  
Sean C. Anderson ◽  
...  
Keyword(s):  
Stock Assessment ◽  
Assessment Method ◽  
Reference Points ◽  
Natural Mortality ◽  
Time Varying ◽  
Fishing Mortality ◽  
Total Allowable Catch ◽  
Robust Approach ◽  
Structured Population Models ◽  
Trade Offs

Abstract A typical assumption used in most fishery stock assessments is that natural mortality (M) is constant across time and age. However, M is rarely constant in reality as a result of the combined impacts of exploitation history, predation, environmental factors, and physiological trade-offs. Misspecification or poor estimation of M can lead to bias in quantities estimated using stock assessment methods, potentially resulting in biased estimates of fishery reference points and catch limits, with the magnitude of bias being influenced by life history and trends in fishing mortality. Monte Carlo simulations were used to evaluate the ability of statistical age-structured population models to estimate spawning-stock biomass, fishing mortality, and total allowable catch when the true M was age-invariant, but time-varying. Configurations of the stock assessment method, implemented in Stock Synthesis, included a single age- and time-invariant M parameter, specified at one of the three levels (high, medium, and low) or an estimated M. The min–max (i.e. most robust) approach to specifying M when it is thought to vary across time was to estimate M. The least robust approach for most scenarios examined was to fix M at a high value, suggesting that the consequences of misspecifying M are asymmetric.

Differences in predicted catch composition between two widely used catch equation formulations

2009 ◽  
Vol 66 (1) ◽  
pp. 126-132 ◽  
Author(s):  
Trevor A. Branch
Keyword(s):  
Age Groups ◽  
Correct Choice ◽  
Fishing Gear ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Gear Selectivity ◽  
Different Types ◽  
Catch Composition ◽  
Continuous Formulation ◽  
Discrete Formulation

Fishing gear selectivity varies among different types of fish (e.g., species, age, sex, or length groups), but their relative catch composition also depends on the fishing process. The continuous (Baranov) formulation assumes that fishing mortality and natural mortality occur together during the fishing season and that there are multiple encounters between fish and fishing gear. For this formulation, predicted catch composition depends on fishing mortality, and at high fishing mortality levels the entire population can be caught provided the selectivity is nonzero for all age groups. In contrast, the discrete formulation assumes that fishing mortality occurs separately from natural mortality and that fish encounter at most only one set of fishing gear. The discrete formulation is easier to compute, but the predicted catch composition is independent of fishing mortality, and some of the population remains unexploitable. The correct choice of equations depends on the particular fishery and fishing mortality levels; at low fishing mortality levels the predictions differ little, but at high fishing mortality levels where multiple gear encounters could occur, the continuous formulation is preferable.

The Effect of Reduction of Fishing Effort on Yield

1962 ◽  
Vol 19 (4) ◽  
pp. 521-529 ◽  
Author(s):  
Syoiti Tanaka
Keyword(s):  
Mortality Rate ◽  
Sudden Change ◽  
Japan Sea ◽  
Fish Population ◽  
Fishing Effort ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Yield Curves ◽  
Before And After ◽  
Steady Level

When a fish population has been depleted by heavy exploitation, with the yield from the population maintaining an unfavourable level, it is usual to expect that the situation will be improved by reduction of fishing effort. Following a sudden reduction of fishing mortality, p, from p1 to p2 at time τ = 0, the yield at once decreases and then increases gradually until it reaches another steady level higher than the former level.The present paper deals, using Baranov's model, with the transition stage of the population following a sudden change in p, as well as with the steady state before and after the change. Relations between equilibrium yield and fishing mortality rate (effort-yield curves) are calculated for various values of the parameters, λ0 (= l0/u, where l0 is the length of a recruit and u is the yearly increase in length), q (natural mortality rate), and b (remaining life span of a fish at the time of recruitment) (Fig. 2). It is noteworthy that for species that grow slowly after recruitment, i.e. when λ0 is large, reduction of fishing would have scarcely any effect on the yield (Fig. 4).Yield curves for the period of transition from the present to various lower levels of fishing are calculated for the case in which λ0 = 4, q = 0.15, b = 10 and p1 = 1.35. These represent parameters for the present state of the stock of sohachi flounders Cleisthenes herzensteini (Schmidt), in the southwestern area of the Japan Sea (Fig. 5).Possible density effects on growth rate and natural mortality rate, which are briefly discussed, appear to diminish considerably the effectiveness of any reduction in fishing effort (Fig. 6).

scholarly journals Multiyear tagging studies incorporating fishing effort data

1998 ◽  
Vol 55 (6) ◽  
pp. 1466-1476 ◽  
Author(s):  
John M Hoenig ◽  
Nicholas J Barrowman ◽  
William S Hearn ◽  
Kenneth H Pollock
Keyword(s):  
Mortality Rate ◽  
Additional Data ◽  
Survival Rates ◽  
Fishing Effort ◽  
Reporting Rate ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Recovery Rates ◽  
Sampling Survey ◽  
Tag Shedding

The Brownie models for multiyear tagging studies can be used to estimate age- and year-specific annual survival rates and tag recovery rates. The latter are composites of the exploitation rates and rates of tag reporting, tag shedding, and tag-induced mortality. It is possible to estimate the exploitation rates if the other components of the tag recovery rates can be quantified. Instantaneous rates of fishing and natural mortality can be estimated if information is available on the seasonal distribution of fishing effort. The estimated rates are only moderately dependent on the timing of the fishing; consequently, the relative effort data can be crude. Information on the timing of the catch over the course of the year can be used as a substitute for the effort data. Fishing mortality can also be assumed to be proportional to fishing effort over years; consequently, if fishing effort is known then the tag reporting rate, natural mortality rate, and a single catchability coefficient can be estimated (instead of natural mortality and a series of fishing mortalities). Although it is possible in theory to estimate both the tag reporting rate and the natural mortality rate with all of these models, in practice it appears necessary to obtain some additional data relating to tag reporting rate to obtain acceptable results. The additional data can come from a variable reward tagging study, a creel or port sampling survey, or from tagged animals that are secretly added to the fishers' catches.

scholarly journals Estimating natural and fishing mortality and tag reporting rate of southern rock lobster (Jasus edwardsii) from a multiyear tagging model

2001 ◽  
Vol 58 (12) ◽  
pp. 2490-2501 ◽  
Author(s):  
S D Frusher ◽  
J M Hoenig
Keyword(s):  
Mortality Rates ◽  
Fishing Effort ◽  
Reporting Rate ◽  
Standard Errors ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Rock Lobster ◽  
Relative Standard ◽  
Jasus Edwardsii ◽  
Mortality Estimates

Fishing and natural mortality rates and tag reporting rate for rock lobsters (Jasus edwardsii) in northwest Tasmania, Australia, were estimated using multiyear tagging models. These estimates are necessary for assessment of the resource. Several models were examined that had either two or three tagging events each year, and either combined sexes or kept sexes separate. The model that best described the dynamics of the fishery utilized three tagging events within a year. The year was divided into discrete periods and, within each year, fishing effort and duration of period were used to apportion fishing and natural mortalities, respectively, to the periods. The separation of fishing mortalities by sex was not found to improve the models. Although high (1.0–1.2·year–1), the instantaneous fishing mortality estimates were comparable to estimates obtained from other methods and the relative standard errors were low. Reporting rate estimates were also precise and indicated a lack of participation by the fishing industry. Estimates of natural mortality were low (0.00–0.02·year–1) but imprecise.

scholarly journals BEBERAPA PARAMETER POPULASI UDANG PUTIH (Penaeus merguiensis de Mann) DI PERAIRAN TARAKAN, KALIMANTAN UTARA

2017 ◽  
Vol 9 (2) ◽  
pp. 85
Author(s):  
Umi Chodrijah ◽  
Ali Suman
Keyword(s):  
Mortality Rate ◽  
Total Mortality ◽  
Fishing Effort ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Population Parameters ◽  
Spawning Period ◽  
Exploitation Rate ◽  
First Maturity ◽  
Penaeus Merguiensis

Tingkat eksploitasi udang putih (Penaeus merguiensis) sangat intensif. Hal ini terindikasi dengan hasil tangkapan udang di WPP-NRI 716 selama 9 tahun terakhir meningkat. Tujuan penelitian ini untuk mengkaji beberapa parameter populasi dan aspek biologi udang putih di perairan Tarakan. Data panjang karapas dan tingkat kematangan gonad udang putih dikumpulkan dari tempat pendaratan udang di Selumit Pantai, Tarakan, Kalimantan Utara pada Januari sampai dengan November 2016. Pendugaan parameter populasi dengan aplikasi model analisis menggunakan program ELEFAN 1. Hasil penelitian menunjukkan rata-rata ukuran udang putih pertama kali tertangkap (Lc) pada panjang karapas 32,51 mm dan rata-rata ukuran pertama kali matang gonad 33,58 mm. Puncak musim pemijahan terjadi pada Maret dan Agustus. Laju pertumbuhan (K) sebesar 1,33 per tahun (betina) dan 1,55 per tahun (jantan). Laju kematian total (Z) sebesar 7,5 per tahun (betina) dan 8,85 per tahun (jantan), laju kematian alamiah (M) sebesar 1,82 per tahun (betina) dan 2,16 per tahun (jantan) serta laju kematian akibat penangkapan (F) sebesar 5,68 per tahun (betina) dan 6,69 per tahun (jantan). Laju pengusahaan (E) udang putih di perairan Tarakan adalah sebesar 0,76 per tahun. Hal ini menunjukkan tingkat pemanfaatan udang putih telah mengalami lebih tangkap (overfishing). Kondisi ini menggambarkan perlunya dilakukan pengurangan upaya sekitar 52 %.  The banana prawn (Penaeus merguiensis) have been exploited intensively. For instance, within nine years the number of shrimp production in FMA 716 increased dramatically. This research aims to identify the some population parameters of banana prawn in the Tarakan waters. This research was carried out from January to November 2016. Data were analyzed using the analytical model application with ELEFAN I. The result showed that the length at first capture (Lc) of banana prawn was 32,51 mmCL and the length at first maturity (Lm) was 33,58 mm CL. The peak season of spawning period was indicated on March and August. The growth rate (K) was 1,33 /year (female) and 1.55/year (male). Total mortality rate (Z) was 7.5/year (female) and 8,85/year (male), natural mortality rate (M) rate was 1.82/year (female) and 2.16/year (male) and fishing mortality rate ( F) were 5.68/ year (female) and 6.69/year (male). The exploitation rate (E) of banana prawn in the Tarakan waters was 0.76 per year. Therefore, level of existing fishing effort of the banana prawn should reduced about 52 % in the next year.

scholarly journals PARAMETER POPULASI IKAN KAKAP LAUT-DALAM (Etelis radiosus, Anderson 1981) DI PERAIRAN TELUK CENDERAWASIH, PAPUA

2017 ◽  
Vol 8 (2) ◽  
pp. 125
Author(s):  
Nurulludin Nurulludin ◽  
Suprapto Suprapto ◽  
Prihatiningsih Prihatiningsih
Keyword(s):  
Deep Sea ◽  
Scientific Information ◽  
Fork Length ◽  
Fishing Effort ◽  
Length Measurement ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
Growth Coefficient ◽  
Exploitation Rate

Ikan kakap laut-dalam (Etelis radiosus) adalah salah satu sumberdaya demersal ekonomis penting di Indonesia. Informasi ilmiah tentang ikan kakap laut-dalam ini masih sangat jarang, terutama dari kawasan Teluk Cenderawasih bagian Utara Papua. Penelitian ini dilaksanakan bulan Februari – November 2013 di Teluk Cenderawasih. Aanalisis panjang cagak ikan terhadap 3.255 ekor menggunakan software FISAT II, diperoleh beberapa nilai parameter populasi sebagai berikut: laju pertumbuhan (K) sebesar 0,17 per tahun, panjang asimtotik (L ) 108,68 cm FL, laju kematian alami (M) 0,4 pertahun, dan laju kematian karena penangkapan (F) 0,17 per tahun. Estimasi tingkat ekploitasi (E) sebesar 0,30 memiliki pengertian bahwa tingkat pemanfaatan ikan kakap laut dalam masih di rendah dan dapat ditingkatkan. Deep-sea snapper (Etelis radiosus) is one of high economic valued of demersal resources in Indonesia. Scientific information on deep-sea snapper is limited, especially from the northern part of Cenderawasih Gulf, Papua. This paper aims to determine some parameters populations of deepsea snapper (Etelis radiosus) in the gulf of Cenderawasih, Papua. The research conducted in February - November 2013 in the Gulf of Cenderawasih. Deepsea snapper fork length measurement randomly taken from 3.255 fishes in Nabire. The result obtained that the growth coefficient (K), asymptotic length (Linf)), natural mortality (M), fishing mortality (F) and exploitation rate (E) were 0.17/ year, 108.68 cmFL, 0.4/year, 0.17/year and 0.30/year. That implied the deepsea snapper fishing exploitation is under exploitation and there possibility of precountionary increasing of fishing effort.

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