These are the lecture notes from the first lecture of my Marine Ecology course (BIOL 462) at UNC last fall. I dumped Blackboard and just started using WordPress to share lectures with my students. It works pretty well, but moving all my lecture content from PowerPoint to WP was a pain (especially for my TA). Benefits include greater ease in incorporating multi-media and outside resources via links and no need for students to download massive PDF or ppt files. And you can also share lectures with the world! Speaking of digital teaching resources for marine ecology, check this out.
Required readings for this lecture: Two articles on declining tuna (here and here and go here if you don’t know anything about bluefin tuna). Also, as supplemental reading, take a look at some of the other stories on fishing at SeaMonster here.
Changing perceptions about our impact on the sea
Global declines in marine fisheries (from Myers and Worm 2003)
- Industrial fisheries typically reduce community biomass within 15 years of exploitation
- Large predatory fish biomass is only about 10% of pre-industrial levels
- Management based on recent data alone can be misleading
- Population baselines are probably much higher than we assumed
Overfishing of shark populations (from Baum et al. 2003)
- Some species have declined 75% over the last 15 years
- Caused by both bycatch and directed fisheries
- All recorded species except 1 has declined by 50%
- Sharks have a very low intrinsic rate of population increase
- Many species are at risk for large scale extinction
Big, long-lived and valuable
From this paper. Read more about the IUCN red list here and here.
One criticism of the IUCN evaluation process and of the study findings is (from here):
Their concerns focus on the IUCN’s “rate of decline” criterion. This compares the rate at which a population is decreasing to the age at which individuals in the population reach sexual maturity (between 5 and 20 years for tunas). The team describes two cases where uncritical application of the rate-of-decline criterion could lead to misleading threat assessments for tunas and billfishes. One is when a population maintains a low but steady level following an earlier precipitous drop due to overfishing. Uncritical application of the rate-of-decline criterion in this case would underestimate threat by placing the population in the “least concern” category, when it may well be vulnerable to extinction in the long term due to genetic effects and natural fluctuations.
The second case would overestimate the threat to a population. This could occur if the IUCN rate-of-decline criterion were applied to a previously un-fished or “virgin” stock that had been quickly culled to a level matching its “maximum sustainable yield” — the goal of fishery managers attempting to ensure the largest on-going harvest. Rapid depletion of a population to its maximum sustainable yield — typically 40-50% of the virgin stock for tunas — would place it in the vulnerable category on the IUCN Red List, directly contradicting a fishery manager’s view that this is a well-managed and sustainable fishery.
Ode to the Stellers Sea Cow
Now on to bluefin tuna
Note NOAA recently declined to designate bluefin tuna as “endangered” under the US ESA (go here).
Bluefin landings, from the NOAA bluefin tuna fact sheet (here)
Back to shifting baselines note the live links to the video about this, just click on the picture!
note the live links to the audio about this, just click on the picture!
The Impact of Recreational Fisheries (from Coleman et al. 2004)
- Study contradicts previous estimates of recreational catch (2%)
- Used NMFS and other databases
- Compared catch of “populations of concern” = those populations listed by NMFS as overfished
- For some important and overfished species, recreational catch was greater than commercial catch:
- Red snapper in the Gulf of Mexico: 59%
- Red drum in the South Atlantic: 93%
- Recreational fishery is focused on higer trophic levels
- link to NPR story here
MSY see here and here for background and read about carrying capacity and logistic growth on the EoE.
[vimeo]http://vimeo.com/9128747[/vimeo]
[vimeo]http://vimeo.com/1772021[/vimeo]
Leave a Reply