Categories of fish. 1. Demersal: live on or near the ocean floor (cod, halibut, flounder, hake, shrimp, and shelfish)

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1 Lecture Fisheries

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3 Categories of fish 1. Demersal: live on or near the ocean floor (cod, halibut, flounder, hake, shrimp, and shelfish) 2. Pelagic: tend to congregate in schools near the ocean surface (herring, anchovies, salmon, mackerel, and tuna)

4 Gear used in demersal fishery 1.Otter Trawl - also known as dragging. A large net is dragged along the bottom. Over the past several years there has been a growing concern about the impact that intensive trawling and/or dredging activities have on the habitat on the sea bottom.

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6 2. Long line or baited hook - a commercial fishing technique that uses hundreds or even thousands of baited hooks hanging from a single line.

7 3. Gill nets Fish try to swim through deliberately sized mesh openings in a hanging net but are unable to squeeze through. They are prevented from backing out due to the tendency for their gills to become caught. This effectively traps them.

8 4. Other devices include fish traps for species such a crab and lobster.

9 Tuna Respond to Primary Production

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11 Collapse: End of Global Fish Stock by 2050? (source: Globalization 101.org, the Levin Institute) FAO estimates that over 70 percent of fish species are currently in danger of collapse. Monitoring 600 groups of fish species, the FAO deems 52 percent to be fully exploited, 17 percent overexploited, 7 percent depleted, and 1 percent recovering. 11

12 Collapse: End of Global Fish Stock by 2050? (source: Globalization 101.org, the Levin Institute) Study using historical analysis projects the collapse of all fish stocks worldwide by Scientists examined fish catch reports from for 64 ocean-wide regions that represented 83 percent of fish species in the world. The biodiversity of 48 marine reserves and areas near fishing grounds were then examined. The collapse, a decline of over 90 percent of stock, of one fish species can threaten an entire marine system. The reduction of biodiversity impairs an ecosystem s ability to recover from environmental stresses and promotes instability. 12

13 Projections of 13

14 US NOAA Fish Stock Sustainability Index Overfishing Harvest rate is above a prescribed fishing mortality threshold. Overfished - Stock size is below a prescribed biomass threshold. Approaching Overfished Condition - Based on trends in harvesting effort, fishery resource size, and other appropriate factors, it is estimated that the fishery will become overfished within 2 years. 14

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16 Fishing down the foodweb

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19 1. Unit Stock : Fish Stock 2. Hydrographic containment : matching of spawning sites to subsequent larval-drift patches assist in preserving the population - Stocks at many mating sites are genetically distinct - Spawning site fidelity ex) northeast Artic cod, Norwegian coastal cod - means gene flow is slow

20 Fish Stock

21 Stock Stock change = recruitment + Growth - Natural mortality - Fishing mortality Stock size is difficult to measure CPUE (Y/X) Yield (Y) per unit fishing effort(x) - quasi-parabolic function of stock size - right drop in curve(why?) 1) competition 2) Large number of larvae will limit resource 3) large number of larvae attract predators

22 Recruitment

23 Length is exponential function of age Growth

24 Rate of growth follows hyperbolic function of age Growth

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27 Difficult to estimate Use of tagging method M=(TL/TR)Y N= Y + (T-TR)Y/TR Where TL, TR, N for stock, Y is Yield, M mortality Natural mortality

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30 Maximum Sustainable Yield Biomass (x) Growth Rate Carrying Capacity (k) time x MSY x Stock that gives maximum sustainable yield 30

31 MSU -problems MSY (Maximum Sustainable Yield) : The largest longterm average catch or yield that can be taken from a stock or stock complex under prevailing ecological and environmental conditions. Purely derived from Logistic Model Difficult to estimate K K can change over time due to conditions Growth rate also difficult to estimate

32 Schäfer-Gordon model -Economically Sustainable Yield Gordon (Journal of Political Economy 1954), Schäfer (1957), Scott (JPE 1955)

33 Economically Sustainable Yield F(X) = Rx(1- x/k) ; Recruitment R : intrinsic growth rate x: fish stock K: carrying capacity of the ecosystem Harvest function (Yield, H) = qex E: Fishing effort q: Catchability

34 Maximum Sustainable Yield F(X) = H => Rx(1- x/k) = qex => R(1- x/k) = qe x = K(1 qe R H= qex = qek(1-qe/r) dh/de=0=qk-2q 2 EK/R => E msy =R/2q )

35 Steady state harvest Insert steady state stock into production function : x = K(1 qe R h = qex ) h = qek(1 qe R ) h is Yield Y

36 Economics Assumptions: Fish price per kg (p) constant Unit cost of effort c constant (constant marginal cost). *Note marginal revenue not constant.

37 Maximum Economic Yield Maximise economic yield by choosing E. qe π = ph ce = pqek(1 ) ce R π = E 2qE pqk( 1 ) c = R 0 E* = R 2q cr R c = (1 2 2 pq K 2q pqk )

38 Pasco et al 2014

39 Open access Unregulated fishing. E.g. no international fisheries agreement. Fishers (countries) enter into the fishery until profits (rent) is equal to zero. 7E

40 Open access effort ph ce = 0 qe pqek( 1 ) ce = R 0 qe pqk( 1 ) c = R E OA = R q 0 Rc R c 2 = (1 pq K q pqk ) If ½ => E OA = MSY in logistic model

41 Two outcomes: Open Access vs. Efficient Rents to the fishery $ TC=C*E TR=p*H(E) TR: total rent TC: total cost MR: marginal rent AR: ave. rent MC: marginal cost AC: Ave. cost $/C w MR AR E Value of fishery maximized at E*. Profits attract entry to E OA (open access) MC=AC E* E MSY E OA E 41

42 Nature 418, (8 August 2002) Towards sustainability in world fisheries Daniel Pauly, Villy Christensen, Sylvie Guénette, Tony J. Pitcher, U. Rashid Sumaila, Carl J. Walters, R. Watson & Dirk Zeller Abstract Fisheries have rarely been 'sustainable'.

43 Mark-Recapture method Sample problem: A pest control technician captures and applies ear tags to 23 brown rats, which he then releases. A week later he traps 29 brown rats, 11 of which have ear tags. What is the estimate of the total population of brown rats?