The New Zealand Best Fish Guide - SEAFOOD Ecolabelling: Principles and Practice - page 377

Table 18.3 ( continued )

Score Technique Environmental effects of technique

D Gillnetting (including set

netting):
e.g. rig shark ( Mustelus
lenticulatus ), elephant
fish ( Callorhinchus milii )

Bycatch and wastage: Gillnetting (including set netting)
has the potential to take large amounts of bycatch
including dolphins, seals, sharks, seabirds and reef fish.
Longer soaking periods lower the chance of unwanted
fish being released alive
Habitat damage: Minimal impact on the seafloor

D Middle-depth trawling:

e.g. hoki, squid, and
southern blue whiting
( Micromesistius
australis )

Bycatch and wastage: Can take substantial tonnage of
bycatch. Trawling catches fur seals, sea lions and
dolphins
Habitat damage: If the seabed is not touched then
impact is minimal, however pelagic trawls often touch
the bottom and therefore have similar impacts to bottom
trawling

E Bottom trawling and

dredging, including pair
trawling
Trawling: e.g. orange
roughy ( Hoplostethus
atlanticus )
Dredging: e.g. oysters
( Tiostrea chilensis ),
scallops ( Pecten
novaezelandiae )

Bycatch and wastage: Trawling and dredging can take
large quantities of bycatch including fish and
invertebrate species, e.g. sponges, corals, etc. Bycatch
in some trawling and dredging can be up to 10 times the
target species. Trawling also catches fur seals, sea lions
and dolphins
Habitat damage: Gear dragged along the seafloor may
cause major habitat damage, increases turbidity and
alters substrate topography. Dredging is particularly
damaging to benthic species

Effectiveness of management and research

Essential fishery information to manage a stock includes:

fish life-history and habitat requirements, for example, maximum age, natural
mortality, age at reproductive maturity (Paul 1992);

the status and trends of fish populations, fishing effort and catch levels;

fishery effects on fish age structure and other marine living resources; and

climate variability effects on larval and juvenile survival and growth.

Table 18.4 Population resilience and productivity parameters.

Productivity parameter

Intrinsic rate von Age at Maximum Natural

Population of increase Bertalanffy Fecundity maturity age mortality Risk

resilience (r)/year k per year (Tmat) (Tmax) (M) rating

> 10 5

Very high > 1 > 0.60 < 1 < 1 > 0.4 A

10 4 -10 5

High 1-0.51 0.31-0.60 1-2 2-3 0.2-0.4 B

10 2 -10 3

Medium 0.16-0.50 0.16-0.30 2-4 4-10 0.1-0.2 C

10-10 2

Low 0.05-0.15 0.05-0.15 5-10 11-30 0.05-0.1 D

Very low < 0.05 < 0.05 < 10 > 10 > 30 < 0.05 E