Habitat quality and fish populations: impacts of nutrient enrichment on the value of European perch off the east coast of Sweden


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Degradation of marine ecosystems through, e.g., eutrophication and climate change is a concern for sustainable fishery management worldwide, but studies on associated impacts on fish populations are rare. This study examines the effects of eutrophying nutrient loads on the economic value of perch populations along the Swedish east coast by estimating the effects of nutrient loads on the population of perch and, then, simulates the harvest value of future perch population under the changes in nutrient loads. A modified Gordon-Schaefer logistic growth model was used for econometric estimation of perch populations based on annual time series data for the period of 1970-2014. Regression analysis using the fully modified ordinary least square (FMOLS) estimator revealed that phosphorus loads had significant effects on the perch population. A 40% decrease in phosphorus loads, as suggested by the international HELCOM agreement, could increase the steady state perch population by 50%. Simple calculations showed that this could increase the total discounted recreational and commercial harvest value of the perch by 30% over a 30 year period.

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    • Fig. 1. Commercial and recreational harvest (tons) of perch off the east coast of Sweden, 1970-2014
    • Fig. 2. Loads (ktons) of (left) nitrogen (N) and (right) phosphorus (P) to the Baltic Sea and the Baltic Proper, 1970-2014
    • Fig. 3. Predicted development in perch population (ton biomass) off the east coast of Sweden in different phosphorus (P) load scenarios
    • Fig. 4. Predicted annual value (million SEK) of the increase in the perch population off the east coast of Sweden over time following a 40% reduction in phosphorus loads to the Baltic Proper, calculated using two different discount rates (0.015 and 0.03)
    • Table 1. Descriptive statistics used in models, observations=45
    • Table 2. Fully modified ordinary least square (FMOLS) estimates of growth function for perch populations off the east coast of Sweden. For abbreviations, see Table 1
    • Table 3. Predicted total discounted values of perch populations for a period of 30 years from 2014 at two different discount rates, r, and phosphorus load scenarios, million SEK
    • Table A1. Results of the augmented Dickey-Fuller unit root test for the regression variables. CV = confidence level
    • Table A2. Results of the Breusch-Godfrey test for serial correlation