Tag Archives: lingcod

Alejandro Frid: rockfish & predation risk theory

Posted on February 10, 2009 by | Leave a comment

Vancouver Aquarium Marine Science Center

Focusing on quillback rockfish and interactions with one of their prey, 3 genera of demersal shrimp which show strong spatial association.  An example from 8 reefs in Howe Sound and adjacent Georgia Strait, depths 14-25m, daytime, 10 Jul – 18 Nov, 2008

Lingcod are the main predator of quillback rockfish.  Estimated biomass in Strait of Georgia down 90% in last 100 years, majority in Howe Sound are <75cm.  Smallest quillback should have strongest avoidance of encounters with lingcod at the expense of access to the shrimp.  Counts per minute (CPM) of small quillbacks rise with shrimp and fall with lingcod.  Large quillback CPM also rises with shrimp, but doesn’t alter with rising lingcod.

If we control for structural complexity of the habitat, then shrimp CPM decreases with rising activity of rockfish.

Predators should be managed not for demographic persistence alone, but for the maintenance of risk-driven ecological processes.

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Posted in 2009 Puget Sound Georgia Basin conference, fish

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Eric Eisenhardt: Efficacy of bottomfish recovery zones

Posted on February 10, 2009 by | Leave a comment

We have a great op in the San Juan Islands to compare marine reserves set up in ~1990 (mandatory) with bottomfish recovery zones (BRZ) were established ~7 years later (voluntary).  Overall, regulations have changed over time, essentially getting more restrictive.

Methods: 300 dives since 1997; transects to compare recovery zones with paired (nearby) reserve

lingcod length: bigger in reserves (2001-2002), but not significantly differnt in 06-07.  Same results with copper rockfish.

populations declining over this period 01-07, except black rockfish which have increased in population and size.

Why aren’t BRZs working better?

  • Using substrate maps, we can see that BRZs have similar areas to the the reference sites and actually have proportionally more rocky habitat.
  • Fishing effort is pretty even over all (e.g. along the west side of San Juan Island, Pile Point and Lime Kiln are about the same as Eagle Point)
  • Compliance issues may be the problem, or the size of the BRZs may be too small

It’s been 10 years.  What shall we do next?

  • Change nothing
  • One larger BRZ?
  • Make BRZs mandatory
  • Make them larger and mandatory

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Anne Beaudreau on lingcod in the San Juan Islands

Posted on February 10, 2009 by | Leave a comment

What are the interacting relationships between rockfish, the lingcod that eat them, and the fishers who take lingcod (and rockfish)?  In reserves we can look at predatory role of lingcod without fishing pressure.  We can also look at differences in lingcod population structure and feeding between non/reserves.

Most samples from central San Juan Channel in rocky habitat.

Body size:

  • non-reserve: 35-80cm, mean ~45cm
  • reserve: quite a few large females, 80-120cm.

Catch rate: in reserves we had many more days when we caught >3 lingcod/hour.

Acoustic telemetry synopsis

  • Limited movement: 8/9 tagged lingcod never left reserve
  • Diet composition: rock fish are 20% of diet in reserves, only 5% in non-reserves (maybe because there are more rockfish in reserves, or maybe larger rockfish in reserves eat more rockfish, or maybe there are habitat differences)
  • Estimated rockfish consumption (modeled): consumption of rockfish in reserves may have been 5x non-reserve, with implications for how to recover rockfish!

Conclusions:

  • Pop structure differs between non/reserves
  • diet variations suggest local diffs in fish communities
  • there are unexpected ecological consequences of creating reserves…
  • match scales of research and management (got to get down to pretty small scales!)

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Posted in 2009 Puget Sound Georgia Basin conference, fish

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