Human interactions and Fisheries

Fisheries science Fisheries management is all about modelling (predicting) the likely [blank_start]size or biomass of target[blank_end] fish species of distinct size/age classes Critical factor is the [blank_start]recruitment[blank_end]. Recruitment – number of fish reaching a certain [blank_start]age/size[blank_end] or [blank_start]position in the life cycle[blank_end] - when they enter the fishery.

Stock assessment Fundamental basics – level of fishing [blank_start]mortality[blank_end] must be balanced by [blank_start]recruitment[blank_end] and [blank_start]growth[blank_end] If max mortality level is exceeded, stock will [blank_start]fall[blank_end], and capacity to [blank_start]rebuild[blank_end] will be reduced

Important terms: Recruit: A fish that [blank_start]survives[blank_end] from egg until reproductive (or legal fishery) age [blank_start]Yield[blank_end]: numbers of fish (or value) produced by the recruits and available to the fishery Collapse – point where a fished population or stock cannot [blank_start]sustain itself[blank_end]. May be arbitrarily set at [blank_start]10%[blank_end] of pre-fished biomass (or 50% MSY) [blank_start]Stock[blank_end] – part of a species population that is reproductively isolated and managed as a single unit

Fishery at MSY In theory, fishing at MSY is desirable for all: Keeps fishing level and stock size relatively high – approx. [blank_start]50%[blank_end] of maximum stock size Management aim is to regulate fishing to keep population size at MSY

Summary MSY and stock assessment Typically fishing at MSY keeps the biomass lower (c. 50-75% lower) than the unfished biomass – Fishing to MSY is risky – if the [blank_start]environment[blank_end] changes it can be easy to [blank_start]overestimate[blank_end] MSY MSY usually estimated by species – but species interact: [blank_start]ecosystem[blank_end] approach may be better…

Growth in fish supply outpaces [blank_start]population growth[blank_end] (3.2% per year vs 1.6% per year) Mostly met by aquaculture, mostly in [blank_start]China[blank_end]

Global marine capture c. 80 million tonnes: 10% [blank_start]tuna and tuna-like[blank_end] species Expansion in NW and WC Pacific, Indian Oceans, contraction in Atlantic and Mediterranean [blank_start]58 Million[blank_end] people engaged in capture fisheries worldwide

aquaculture [blank_start]6%[blank_end] growth per year: 94 million tonnes in 2012, of which 66 Million tonnes is food fish, 23 Million tonnes aquatic algae. China c. [blank_start]50%[blank_end] of global production 20 million people are engaged in aquaculture (>90% in China)

social Fish capture and production large source of [blank_start]employment[blank_end] for women (especially in developing countries) More than 15% primary capture employment women and up to 90% processing employment Fishing and aquaculture assure livelihoods of c. [blank_start]10%[blank_end] of world’s population

Trends – doom and gloom? Collapsed species Fishing down food chain Fishing deeper Loss [blank_start]apex predators[blank_end] PP utilized

Types of fishery data: Research survey - [blank_start]Highest resolution[blank_end] – direct measure of biomass for all species collected in the survey. Limited [blank_start]focus[blank_end], few comparative datasets [blank_start]Stock assessment[blank_end] - Estimate of biomass for specific populations of species based on survey and catch effort data – only data on few targeted species Catch data - Reported biomass of [blank_start]landed species[blank_end]. Global in scope, but does not reflect [blank_start]discards[blank_end] and IUU, and is influenced by accidental and deliberate [blank_start]mis-reporting[blank_end], changes in regulation and markets.

Catch data do not track biomass because other things can influence catch (e.g. changes in [blank_start]restrictions[blank_end], market prices for specific species, [blank_start]fuel[blank_end] prices, vessel exclusions, population [blank_start]shifts[blank_end]). Also, in a random stationary time series, maximum catch is likely to [blank_start]increase[blank_end] with a longer time series (so more chance of having collapse figures over time)

Summary so far Estimating how many fish have been caught is difficult Catch and effort data are biased in complex ways as these reflect [blank_start]socio-economics[blank_end] and [blank_start]geopolitics[blank_end] as well as ecology/biology Satellite and big data approaches are changing the way we understand, measure and police global fishing efforts

Fishing effects Direct removal of target species Changes in [blank_start]size[blank_end] structure of target populations Alterations to [blank_start]non-target[blank_end] populations of fish and benthos Alterations to physical environment Food chain effects (trophic [blank_start]cascades[blank_end], altered [blank_start]predation[blank_end] pressure)

Fishing down (through) the food chain Pauly et al (1998). Fishing Down Marine Food Webs. Science 279: 860-863. Most food fish were trophic levels 4.0-4.5 Argument that we are now moving our predation [blank_start]down a trophic level[blank_end] from 4 to 3 (fishing down). Also by removing predators, [blank_start]low[blank_end] trophic level biomass expands, decreasing mean TL (fishing through)

Alternative : Catch TL is not the same as ecosystem TL Theoretical comparison based on simulation ecosystem [blank_start]models[blank_end] (week 3) Catch TL poor reflection of ecosystem TL when catch is [blank_start]selective[blank_end] within the food web

Recent data from research trawls are suggesting that deep-sea fish species (including by-catch) biomass is [blank_start]on the decline[blank_end].

Summary: state of world fish Globally, best estimate is that c. [blank_start]30%[blank_end] of fish stocks are over fished, [blank_start]60%[blank_end] are fully exploited, and 10% are underexploited Aquaculture provides [blank_start]more[blank_end] fish than capture fisheries Long history of management failure, stock collapse. Current ecosystems have low [blank_start]abundance[blank_end] and [blank_start]diversity[blank_end] with [blank_start]small[blank_end] body sizes. Top predators heavily [blank_start]depleted[blank_end] Catch data easily available but may give [blank_start]flawed[blank_end] picture of ecosystem state and trends Rebuilding occurring in heavily regulated fisheries [blank_start]Satellite[blank_end] vessel monitoring and big data processing give us a much richer view of fishing effort More to be done in developing world fisheries

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