Myfish

Scientific Publications

    Below (in alphabetic order by Author) publications acknowledging the Myfish project

     
    Author(s):Da Rocha J.M., Cerviño S., Villasante S.
    Title:The Common Fisheries Policy: An enforcement problem
    Abstract:Marine populations in Europe are in decline due to the unsuccessful results of the Common Fisheries Policy. By combining data of scientific recommendations from ICES, TACs approved and reported landings with an age-structured model, the objectives of this paper are to investigate the level of compliance of the TAC regulation, and the level of enforcement and its economic impact on fishery resources. The results presented here suggest that while there does not exist a regular pattern between TAC proposal and TAC approved, there is a clear pattern between TAC approved and reported landings. As a consequence, there is a regular lack of enforcement at national fisheries authority level. The paper also presents results of the recovery plans for the Southern hake and the Atlantic cod fisheries as case studies to illustrate the level of enforcement based on collusion between national fisheries advisers and industry. The results from both cases studies analyzed here indicate that drastic solutions could generate positive results for the recovery of the stocks, but perhaps they are not always the best measure in fisheries management due to the high economic losses for fishermen and social effects on coastal communities in the short and medium term. Finally, this work demonstrates that if the recovery plans had been implemented, the net present profits for both fisheries would have increased over time.
    Permanent Identifier:http://www.sciencedirect.com/science/article/pii/S0308597X12000425
     
    Author(s):Da Rocha J.M. and Gutiérrez M.J.
    Title:Endogenous Fishery Management in a Stochastic Model: Why Do Fishery Agencies Use TACs Along with Fishing Periods?
    Abstract: This paper seeks to explain the circumstances under which using total allowable catch (TAC) as an instrument to manage a fishery along with fishing periods may be of interest from a regulatory point of view. The deterministic analysis by Homans and Wilen (J Environ Econ Manag 32:1–21, 1997) and Anderson (Ann Oper Res 94:231–257, 2000) is thus extended to a stochastic scenario where the resource cannot be measured accurately. The resulting model is solved numerically to find the optimal control rules in the Iberian sardine stock. Three relevant conclusions can be highlighted from simulations: first, the greater the uncertainty regarding the state of the stock, the lower the probability of the fishery being closed before the end of the fishing period. Second, the use of TACs as a management instrument in fisheries that are already regulated by fishing periods leads to: (i) an increase in the optimal season length and harvests, especially for medium and high numbers of licences; (ii) improved biological and economic variables when the fleet is large; and (iii) extinction risk for the resource being eliminated. Third, the regulator would rather select the number of licences than restrict the season length.
    Permanent Identifier: http://www.springerlink.com/content/524247584nh87766/?MUD=MP

    Author(s):Da Rocha J.M., Gutiérrez M.J. and Antelo L.T.
    Title:Selectivity, Pulse Fishing and Endogenous Lifespan in Beverton-Holt Models
    Abstract:Optimal management in a multi-cohort Beverton-Holt model with any number of age classes and imperfect selectivity is equivalent to finding the optimal fish lifespan by chosen fallow cycles. Optimal policy differs in two main ways from the optimal lifespan rule with perfect selectivity. First, weight gain is valued in terms of the whole population structure. Second, the cost of waiting is the interest rate adjusted for the increase in the pulse length. This point is especially relevant for assessing the role of selectivity. Imperfect selectivity reduces the optimal lifespan and the optimal pulse length. We illustrate our theoretical findings with a numerical example. Results obtained using global numerical methods select the optimal pulse length predicted by the optimal lifespan rule
    Permanent Identifier: http://www.springerlink.com/content/c7gq267n72270317/
     
    Author(s):Da Rocha J.M., Gutiérrez M.J., Cerviño S., Antelo L.T.
    Title: “logMSY” and optimal harvesting control rules: New tools for the implementation of the European Common Fisheries Policy
    Abstract:The reform of the European Common Fisheries Policy (CFP) aims to restores and maintains fish resources at levels which can produce the maximum sustainable yield (MSY) not later than 2015. In this paper we show why if MSY is used as reference point, optimal management may entail pulse fishing. This means that current management of the European fisheries is based on metrics that may generate solutions that would not be accepted as feasible due to the large social costs implied. We discuss why changes in the metrics used to define the reference point (the logMSY) and/or optimal harvesting control rules that stabilize the employment and the biomass around the optimal stationary values are two possible solutions of this paradox. The European Union should take into account all these considerations for the CFP reform proposals.
    Permanent Identifier: http://www.sciencedirect.com/science/article/pii/S0964569112001615
     
    Author(s):Fung T., Farnsworth K.D, Shephard S., Reid D.G., Rossberg A.G.
    Title:Why the size structure of marine communities can require decades to recover from fishing
    Abstract:

    A dynamic food-web model of more than 1000 species was used to quantify the recovery trajectory of marine community size-structure under different hypothetical fishing regimes, using the Northeast Atlantic as an example. Size-structure was summarised by four indicators: the Large Fish Indicator (LFI), the Large Species Indicator (LSI), the biomass-weighted mean maximum length of fish species (EMBED Equation.3) and the biomass-weighted mean maturation length of fish species (EMBED Equation.3). Time-series of these indicators recorded recovery following release from fishing with various size-selectivities, intensities and durations. In model simulations, fishing-induced trophic cascades were observed to distort fish community size-structure, but these did not have a large influence on recovery level or duration as measured by the four indicators. However, simulations showed that local extinctions of large fish species increased in number with both fishing intensity and duration, and could strongly limit the recovery level. Recovery of fish community size-structure to near equilibrium frequently took multiple decades in simulations; these long transient periods suggest that management interventions for size-structure recovery may require much longer than previously thought. Our results demonstrate the need for community-level modelling to set realistic targets for management of community size-structure.

    Permanent Identifier:
     http://www.int-res.com/prepress/m10305.html

    Author(s):Quaas M.F., Froese R., Herwartz H., Requate T., Schmidt J.O., Voss R.
    Title:Fishing industry borrows from natural capital at high shadow interest rates
    Abstract:Fish stocks can be considered as natural capital stocks providing harvestable fish. Fishing at low stock sizes means borrowing from the natural asset. While fishing a particular quantity generates immediate profits and income, an interest rate has to be paid in terms of foregone future fishing income, as the fish stock's reproductive capacity remains low and fishing costs stay high. In this paper we propose to apply the concept of shadow interest rate to quantify the degree of overfishing. It incorporates the relevant biological and economic information and compares across fish stocks. We calculate the shadow interest rates for 13 major European fish stocks and find these rates to range from 10% to more than 200%. The concept of the shadow interest rate can be used to make the economic consequences of overfishing transparent and to evaluate the profitability of short-term catch reductions as investments in natural capital stocks.
    Permanent Identifier:http://www.sciencedirect.com/science/article/pii/S0921800912003072

     
    Author(s):Shephard S., Fung T., Rossberg A.G., Farnsworth K.D., Reid D.G., Greenstreet S.P.R., Warnes S.
    Title:Modelling recovery of Celtic Sea demersal fish community size-structure
    Abstract:The Large Fish Indicator (LFI) is a size-based indicator of fish community state. The indicator describes the proportion by biomass of a fish community represented by fish larger than some size threshold. From an observed peak value of 0.49 in 1990, the Celtic Sea LFI declined until about 2000 and then fluctuated around 0.10 throughout the 2000s. This decline in the LFI reflected a period of diminishing ‘large’ fish biomass, probably related to high levels of size selective fishing. During the study period, fishing mortality was maintained at consistently high values. Average biomass of ‘small’ fish fluctuated across the whole time series, showing a weak positive trend in recent years. Inter-annual variation in the LFI was increasingly driven by fluctuation in small fish biomass as large fish biomass declined. Simulations using a size-based ecosystem model suggested that recovery in Celtic Sea fish community size-structure (LFI) could demand at least 20% reductions in fishing pressure and occur on decadal timescales.
    Permanent Identifier:www.sciencedirect.com/science/article/pii/S0165783612003542

     
    Author(s):Shephard S., Gerritsen H., Kaiser M.J., Reid D.G.
     Title:Spatial Heterogeneity in Fishing Creates de facto Refugia for Endangered Celtic Sea Elasmobranchs
     Abstract:The life history characteristics of some elasmobranchs make them particularly vulnerable to fishing mortality; about a third of all species are listed by the IUCN as Threatened or Near Threatened. Marine Protected Areas (MPAs) have been suggested as a tool for conservation of elasmobranchs, but they are likely to be effective only if such populations respond to fishing impacts at spatial-scales corresponding to MPA size. Using the example of the Celtic Sea, we modelled elasmobranch biomass (kg h21) in fisheries-independent survey hauls as a function of environmental variables and ‘local’ (within 20 km radius) fishing effort (h y21) recorded from Vessel Monitoring Systems data. Model selection using AIC suggested strongest support for linear mixed effects models in which the variables (i) fishing effort, (ii) geographic location and (iii) demersal fish assemblage had approximately equal importance in explaining elasmobranch biomass. In the eastern Celtic Sea, sampling sites that occurred in the lowest 10% of the observed fishing effort range recorded 10 species of elasmobranch including the critically endangered Dipturus spp. The most intensely fished 10% of sites had only three elasmobranch species, with two IUCN listed as Least Concern. Our results suggest that stable spatial heterogeneity in fishing effort creates de facto refugia for elasmobranchs in the Celtic Sea. However, changes in the present fisheries management regime could impair the refuge effect by changing fisher’s behaviour and displacing effort into these areas.
     Permanent Identifier: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0049307

    Why the size structure of marine communities can require decades to recover from fishing

    Tak Fung, Keith D. Farnsworth, Samuel Shephard, David G. Reid, Axel G. Rossberg - Marine Ecology Progress Series (doi:10.3354/meps10305)

    Abstract: A dynamic food-web model of more than 1000 species was used to quantify the recovery trajectory of marine community size-structure under different hypothetical fishing regimes, using the Northeast Atlantic as an example. Size-structure was summarised by four indicators: the Large Fish Indicator (LFI), the Large Species Indicator (LSI), the biomass-weighted mean maximum length of fish species (EMBED Equation.3) and the biomass-weighted mean maturation length of fish species (EMBED Equation.3). Time-series of these indicators recorded recovery following release from fishing with various size-selectivities, intensities and durations. In model simulations, fishing-induced trophic cascades were observed to distort fish community size-structure, but these did not have a large influence on recovery level or duration as measured by the four indicators. However, simulations showed that local extinctions of large fish species increased in number with both fishing intensity and duration, and could strongly limit the recovery level. Recovery of fish community size-structure to near equilibrium frequently took multiple decades in simulations; these long transient periods suggest that management interventions for size-structure recovery may require much longer than previously thought. Our results demonstrate the need for community-level modelling to set realistic targets for management of community size-structure. http://www.int-res.com/prepress/m10305.html

    Modelling recovery of Celtic Sea demersal fish community size-structure

    Samuel Shephard, Tak Fung, Axel G. Rossberg, Keith D. Farnsworth, David G. Reid, Simon P.R. Greenstreet, Steve Warnes (Fisheries Research 140 (2013) 91– 95)

    Abstract: The Large Fish Indicator (LFI) is a size-based indicator of fish community state. The indicator describes the proportion by biomass of a fish community represented by fish larger than some size threshold. From an observed peak value of 0.49 in 1990, the Celtic Sea LFI declined until about 2000 and then fluctuated around 0.10 throughout the 2000s. This decline in the LFI reflected a period of diminishing ‘large’ fish biomass, probably related to high levels of size selective fishing. During the study period, fishing mortality was maintained at consistently high values. Average biomass of ‘small’ fish fluctuated across the whole time series, showing a weak positive trend in recent years. Inter-annual variation in the LFI was increasingly driven by fluctuation in small fish biomass as large fish biomass declined. Simulations using a size-based ecosystem model suggested that recovery in Celtic Sea fish community size-structure (LFI) could demand at least 20% reductions in fishing pressure and occur on decadal timescales. www.sciencedirect.com/science/article/pii/S0165783612003542

    A generalized functional response for predators that switch between multiple prey species

    E.Van Leeuwena, Å. Brännströmb, V.A.A. Jansena, U. Dieckmannc, A.G. Rossberg. (Journal of Theoretical Biology)

    Abstract: We develop a theory for the food intake of a predator that can switch between multiple prey species. The theory addresses empirical observations of prey switching and is based on the behavioural assumption that a predator tends to continue feeding on prey that are similar to the prey it has consumed last, in terms of, e.g., their morphology, defences, location, habitat choice, or behaviour. From a predator’s dietary history and the assumed similarity relationship among prey species, we derive a general closed-form multi-species functional response for describing predators switching between multiple prey species. Our theory includes the Holling type II functional response as a special case and makes consistent predictions when populations of equivalent prey are aggregated or split. An analysis of the derived functional response enables us to highlight the following five main findings. (1) Prey switching leads to an approximate power-law relationship between ratios of prey abundance and prey intake, consistent with experimental data. (2) In agreement with empirical observations, the theory predicts an upper limit of 2 for the exponent of such power laws. (3) Our theory predicts deviations from power-law switching at very low and very high prey-abundance ratios. (4) The theory can predict the diet composition of a predator feeding on multiple prey species from diet observations for predators feeding only on pairs of prey species. (5) Predators foraging on more prey species will show less pronounced prey switching than predators foraging on fewer prey species, thus providing a natural explanation for the known difficulties of observing prey switching in the field. http://www.sciencedirect.com/science/article/pii/S0022519313000611

    flagsThe research leading to these results has received funding from the European Union’s Seventh Framework Programme (FP7 /2007-2013) under grant agreement no 289257. This publication reflects the views only of the author, and the European Union cannot be held responsible for any use which maybe made of the information contained therein.

    powered by  WAZOUR