Fishing Effort & CPUE: BIOL3305 Lecture Notes (PDF)

Fishing effort & CPUE Dirk Zeller Sea Around Us – Indian Ocean  Fishing effort & CPUE Raised last week….. How measure fishing effort? Usually by fleet or gear type, e.g., trawl fleet (Australia’s Northern Prawn Trawl Fleet - NPTF) 1. Nominal effort: e.g....

Fishing effort & CPUE Dirk Zeller Sea Around Us – Indian Ocean  Fishing effort & CPUE Raised last week….. How measure fishing effort? Usually by fleet or gear type, e.g., trawl fleet (Australia’s Northern Prawn Trawl Fleet - NPTF) 1. Nominal effort: e.g., number of boats in a fishery (number of large versus small trawlers in NPTF) 2. Effective effort: takes duration of fishing into account, hours or days fished per year per boat (number of boat-hours trawled per boat per year in NPTF) Works well if only concerned about one fishery/gear Problem: How standardize effort across differing fishing gears and different fisheries, and over time? 2/34 Fishing effort & CPUE Dalzell et al. (1996) Oceanographic Marine Biology Annual Review 34: 395-531 Fishing effort & CPUE Dalzell et al. (1996) Oceanographic Marine Biology Annual Review 34: 395-531  Fishing effort & CPUE 5/34 Dalzell et al. (1996) Oceanographic Marine Biology Annual Review 34: 395-531 Fishing effort & CPUE Dalzell et al. (1996) Oceanographic Marine Biology Annual Review 34: 395-531  Fishing effort & CPUE Kg·line-1·h-1 How many hours fished by how many hand line fishers per day, for how many days per week or year, on average? Kg·man-1·h-1 How many hours fished by how many spearfishers per day, for how many days per week or year, on average? Kg·h-1, Kg·trip-1, Kg·100 m net-1·h-1, Kg·10 m net-1·h-1, Kg·set-1 How many hours fished/trips made/100 m net hours/10 m net hours/sets made by how many gillnet fishers per day, for how many days per week or year, on average? Kg·set-1, Kg·man-1·h-1, Kg·h-1 How many sets /man hours/hours made by how many beach-seine fishers per day, for how many days per week or year, on average? What is the actual total effort being expended for each gear? How can generate overall CPUE across gears and fishing methods? Dalzell et al. (1996) Oceanographic Marine Biology Annual Review 34: 395-531 Fishing effort & CPUE Lynham et al. (2020) Nature Communications 11(1): 979 Fishing effort & CPUE Polacheck (2006) Marine Policy 30: 470-482  Fishing effort & CPUE 10/34 Polacheck (2006) Marine Policy 30: 470-482 How can we standardize fishing effort across all fisheries? What is common to all fisheries? In order to obtain a catch, we must expend “effort” or “intensity of the activity” Widely has been approximated via number of vessels by vessel length… But a 10 m fishing pirogue in Africa does not expend the same fishing intensity/power (effort) as a 10 m bottom trawler in Europe…. Effort = power input or power intensity input…. Engine power is the equalizing and standardizing unit across all fisheries Engine power HP, but not a metric unit 1 HP = 735.5 watts; 1 kW = 1.34 HP Nominal effort: kW by fleet type with a similar capacity, i.e., in the same length class and motorization category, and utilizing the same or similar fishing gears Effective effort: kWdays taking into account total fishing time per year Greer et al. (2019) Marine Policy 107: 103382  How can we standardize fishing effort across all fisheries? For shore-based fishers, engine power equivalent of 0.08 kW Greer et al. (2019) Marine Policy 107: 103382 Zeller et al. (2021) Frontiers in Marine Science 8: 70799  Fishing effort reconstruction - Globally estimate (“reconstruct”) the world’s marine fishing fleet capacity - By fishing sector, vessel size class, gear-type and engine size - Including non-motorized and shore-based - Preliminary… Requires future data vetting, refinements, corrections & improvements Country-specific reconstructions - Online accessible via fishing country; 1950-2010, post-2010 updates questionable - Caveats Sectoral definitions may not align between effort and catch Spatial coverage differs: EEZ versus fishing country (not an issue for SSF) Greer et al. (2019) Marine Policy 107:103382 Greer et al. (2019) Marine Policy 107:103491  Fishing effort reconstruction Industrial fleet type may or may not fish in American Samoan EEZ  Catch per unit of effort (CPUE) Overall, across fisheries, gears and area for West Africa 15/34 Belhabib et al. (2018) Conservation Letters 11(1): e12360 Catch per unit of effort (CPUE) Zeller et al. (2021) Frontiers in Marine Science 8: 70799  Catch per unit of effort (CPUE) Countries Comoros Islands Madagascar Mayotte Mozambique Small-scale fisheries only French Mozambique Channel Islands excluded as uninhabited Large-scale/industrial not considered (domestic or foreign) Zeller et al. (2021) Frontiers in Marine Science 8: 70799 Effort (Comoros) Zeller et al. (2021) Frontiers in Marine Science 8: 70799 Effort (Madagascar) Zeller et al. (2021) Frontiers in Marine Science 8: 70799  Effort (Madagascar) Zeller et al. (2021) Frontiers in Marine Science 8: 70799 20/34 Effort (Mayotte) Zeller et al. (2021) Frontiers in Marine Science 8: 70799 Effort (Mozambique) Zeller et al. (2021) Frontiers in Marine Science 8: 70799 Effort (Mozambique) Zeller et al. (2021) Frontiers in Marine Science 8: 70799  Effort reconstruction Reconstructions Considerable research effort & time required Deep and detailed search for, understanding and interpretation of information Careful vetting for applicability and caveats Implementation and use requires assumptions Detailed documentation (Supplementary Materials & Technical Reports) ‘Dirty’ data problem is guaranteed (see last week’s Lab talk), and requires ongoing vetting and verification Zeller et al. (2021) Frontiers in Marine Science 8: 70799  Effective effort Zeller et al. (2021) Frontiers in Marine Science 8: 70799 25/34 Reconstructed catches Zeller et al. (2021) Frontiers in Marine Science 8: 70799  CPUE Overall 91% decline in CPUE 174 kg·kWday-1 in 1950 15 kg·kWday-1 by 2016 Each country Strong impact of motorization Massive growth in number of boats Only through our standardization are such comparative studies possible Between fisheries Between gear-types Between countries, regions & globally Zeller et al. (2021) Frontiers in Marine Science 8: 70799 Catch per unit of effort (CPUE) Derrick et al. (2023) Frontiers in Marine Science 10: 1201661  Catch per unit of effort (CPUE) Rely heavily on small-scale fisheries Little agriculture, high poverty rate Data reporting & management consistently incomplete or lacking Islands very high biodiversity & endemism “Galapagos Islands of the Indian Ocean” Large-scale/industrial not considered (domestic or foreign) Likely high in offshore waters (tuna) Derrick et al. (2023) Frontiers in Marine Science 10: 1201661  Catches Post-1991 Gulf War repatriations from Saudi Arabia… high migration to islands By early 2000s, long-term overfishing by SSF fleets… catch declines 2010s, Yemen internal conflicts … decrease artisanal, turning to subsistence Derrick et al. (2023) Frontiers in Marine Science 10: 1201661 30/34  Effort & CPUE Massive development initiatives 1960-1980… motorization of fleets Response to declining catches starting in 2000….. more boats Result: By mid-2000s rapid and strongly declining CPUE… stocks overfished or at high risk of over-exploitation (supported by independent research) Derrick et al. (2023) Frontiers in Marine Science 10: 1201661  Summary: Effort & CPUE Fishing effort data (units) are highly diverse - Due to the nature of stock assessment focus being fishery or gear specific Need for standardization if cross-fishery or large spatial comparisons of interest - Hence Sea Around Us use of standardized kWday Standardized CPUE of use as first order indicator of broad changes in the underlying resource “(relative) abundance over time”… Sea Around Us – Indian Ocean