Fisheries Management and Ecology

New Zealand Fisheries Overview and Key Statistics

• Geographical Facts:

  • Land Area: $270,534\,km^2$.

  • Water Area (EEZ): $4,053,000\,km^2$, making it the world’s 4th largest Exclusive Economic Zone.

  • Continental Coastline: $15,650\,km$ in length.

  • Bathymetry: approximately $72\%$ of New Zealand's waters are deeper than $1000\,m$.

• Economic Impact (2022 Data):

  • Fisheries GDP: $2.2\text{ billion}$.

  • Contribution to National GDP: $0.7\%$.

  • Employment: approximately $16,528$ jobs.

• Production and Trade:

  • Fish Production (Total Allowable Commercial Catch - TACC): $591,000\text{ tonnes}$.

  • Key Fishing Grounds: The Chatham Rise and Subantarctic regions account for $60\%$ of the total fish caught.

  • Exports: $238,864\,t$.

  • Global Context: New Zealand contributes $1\%$ of world fish production but represents $2\%$ of global trade.

Fundamental Principles of Fisheries Management

• Response to Fishing Pressures: Management systems are designed to address increasing fishing pressure (overfishing) and the expansion of fishing fleets, which often leads to over-capitalization.

• Regulatory Evolution: Regulation has moved from diverse, somewhat arbitrary rules toward more structured systems. A primary reference for this evolution in New Zealand is Sissenwine, MP and Mace, PM (Fishery Bulletin US, 90, 147-160), discussing the era of fixed quota in perpetuity.

• Historical Context: New Zealand saw an exponential increase in fishing catch starting around $1970$.

The Individual Transferable Quota (ITQ) System

• Definition of ITQ: Individually Transferable Quotas are rights set as a percentage of the Total Allowable Commercial Catch (TACC). They assign ownership of portions of the TACC to individual commercial fishing enterprises, which can then be bought or sold.

• Management Metrics:

  • Total Allowable Catch (TAC): The total quantity of a species/stock that can be sustainably harvested each year.

  • Total Allowable Commercial Catch (TACC): The specific portion of the TAC allocated to the commercial sector.

  • Allowances: Specific portions of the TAC set aside for recreational and customary (Maori) fishing before the TACC is determined.

• Initial Structure: The system originally covered $26$ species-groups across up to $10$ Fishery Management Areas (FMAs).

• Economic Mechanism: Fishing enterprises pay a "Resource Rental" to the New Zealand government.

• Expectations of ITQs:

  • End the "race to fish" and reduce overall fishing effort.

  • Increase economic efficiency by eliminating competition between harvesters for the largest share.

  • Facilitate the removal of excess capital as more efficient operators consolidate quota.

  • Rebuild depleted stocks and encourage responsible industry behavior.

  • Move toward industry co-management with reduced government intervention and political strife.

Fishery Management Areas (FMAs) and Quota Management Areas (QMAs)

• Stock Definition: FMAs/QMAs vary by species and generally correspond to biogeographic regions.

• Management Units: Each area is managed as a separate and distinct "stock" (e.g., BCO3 for Blue Cod or ORH2B for Orange Roughy).

Maximizing Yield and Fisheries Modeling

• Maximum Sustainable Yield (MSY): The Ministry for Primary Industries (MPI) is mandated to maintain fish stocks at or above the level that produces MSY.

• MSY Definition: The greatest yield that can be achieved over time while maintaining the stock's productive capacity.

• Key Parameters:

  • $B_{MSY}$: The biomass level required to support the maximum sustainable yield.

  • Catch-Per-Unit Effort (CPUE): The weight or number of fish taken per defined period of effort (e.g., catch per hour of trawling). It is used as a proxy for stock size.

• Fisheries Model Components: To be effective, models must account for all stages of the life cycle:

  • Reproduction: The creation of new offspring.

  • Nursery area: Habitat for juvenile growth.

  • Recruitment: The process by which new individuals enter the exploitable fishery (often modeled using stock-recruitment relationships and density-dependent effects).

  • Mortality: Natural and fishing-induced deaths.

Mathematical Foundations of MSY and Logistic Growth

• Theory of Surplus Production: MSY assumes that when population density is reduced below carrying capacity ($K$), growth, survival, and reproductive rates remain high, creating a surplus for harvest.

• Logistic Growth Equation:

  • $\frac{dN}{dt} = rN \left( 1 - \frac{N}{K} \right)$

  • Where $N$ is population size, $r$ is the intrinsic growth rate, and $K$ is the carrying capacity.

• Point of MSY:

  • MSY typically occur at the point of maximum population growth rate, which is theoretically at $K/2$ in basic models, though in practice it is often observed at approximately $30\%$ of the unexploited (virgin) population size.

  • This approach harvests the "excess production" that would otherwise lead to population growth.

• Catch-Effort Curve: A theoretical curve showing that catch increases with effort only up to the biologically optimal point (MSY). Beyond this point, increased effort leads to smaller catches due to overexploitation.

Criticisms and Limitations of MSY

• Biological Simplification: MSY often treats all fish as identical, ignoring the importance of size and age structure within stocks.

• Investment Incentives: It can encourage heavy initial investment in vessels to achieve early stock declines toward the MSY target.

• Verification Problem: MSY is often only identifiable once it has been exceeded (overshot).

• Environmental Stasis: It assumes constant annual production and ignores natural environmental variability.

• Ecosystem Impacts: It focuses on single species and often fails to account for effects on the wider ecosystem or other species.

• Technological Advances: Constant improvements in fishing technology can mask stock declines.

• Serial Depletion: The tendency to move from one depleted area to a new one.

The New Zealand Stock Assessment Process

• December – April: Information is gathered and requested to assist the assessment process.

• May: Fishery Assessment Working Groups meet to review data.

• June: Working Group Reports are completed.

• August: Fishery Assessment Plenary occurs; Ministry TAC meetings; TACC Advisory Council; Consultations with the Fishing Industry Board (FIB) and non-commercial user groups (Economic, Environmental, Maori).

• September 15: Advice on TACC changes is provided to the Minister.

• October 1: TACC decisions are made by the Minister and the Quota Adjustment Process begins.

Case Study: Orange Roughy (Hoplostethus atlanticus)

• Biology: A very slow-growing, late-maturing species categorized as a "slow fish" or a classic unproductive K-strategist. They live long lives and do not breed every year.

• History: Known for "boom and bust" or "gold rush" fishing because they aggregate in large numbers around underwater hills/features, making them easy to target with large boats.

• Sequential Depletion: Examples from the East Cape show rapid expansion from $1$ hill in Year 1 to $8$ hills by Year 3 as previous aggregations were depleted.

• Current Status:

  • On the Challenger Plateau, biomass dropped to $\sim 5\%$ of its $1970$ levels.

  • Recovery for such species may take decades to centuries.

  • Current management includes scientific research, voluntary closures, and efforts to reduce impacts on marine habitats and non-target species.

Case Study: Atlantic Cod (Gadus morhua)

• Historical Abundance: In the $1500\text{s}$, stocks were so dense that boats could hardly be rowed through them.

• Technological Shift: Early methods (handline, longline, gillnets) were replaced by bottom trawling, which significantly altered marine habitats.

• The Industrial Era:

  • 1954: Introduction of the first factory-freezer trawler, the Fairtry (UK), on the Grand Banks.

  • 1968: Peak harvest of over $800,000\text{ tons}$, accounting for $40\%$ of global landings.

• The Collapse:

  • 1992: A devastating collapse of stocks off the east coast of Newfoundland led to a fishery closure and the loss of $40,000\text{ jobs}$.

  • 2003: The population was officially declared "endangered" by the Canadian government.

  • Recovery remains limited despite the lack of a targeted fishery.

Evolutionary and Selective Impacts of Fishing

• Phenotypic Changes: Intense fishing pressure has led to measurable evolutionary changes in remaining populations:

  • Reduction in Age-at-maturity: $16\text{--}30\%$.

  • Reduction in Length-at-maturity: approximately $20\%$.

• Implications: These changes are highly significant for the recovery potential of stocks and may be irreversible.