15.1. Introduction
343
tion and ultimate conservation and protection of EFH requires data on fish
population dynamics and the ecological influences of habitat on those dynamics for each life-history stage.
Historically, research on exploited offshore fish populations has been directed toward understanding the dynamics of adults and mortality of
pelagic eggs and larvae (Anderson 1988), whereas the attention of the fisheries management community has focused largely on the management of
adults through traditional controls on fishing effort (e.g . limitations on days
at sea, gear restrictions , and catch quotas) (Sissenwine 1984). Less attention
has been directed to the dynamics of early benthic phase juvenile fish
and the role of habitat in mediating post-settlement processes (e.g. Auster &
Malatesta 1995; Tupper & Boutilier 1995a; Auster et al. 1997) and linkages
between patterns in post-settlement juvenile fish survivorship and the alteration of sea floor habitat by fishing activity (Auster et al. 1996, 1999; Auster
1998;Jennings and Kaiser 1998; Lindholm et al. 1998; Lindholm et al. 1999).
Researchers have observed high densities of settled juvenile cod on the
gravel portion of Georges Bank (Lough et al. 1989), on rocky reefs, sea
grass beds, and gravel of the nearshore environment in Nova Scotia (Tupper & Boutilier 1995 a,b) and over hard bottom in Newfoundland (Gregory
et al. 1997). Although juveniles settle on less complex habitats such as sand,
high post-settlement mortality over habitats with little to no relief lead to
low juvenile survival (Lough et al. 1989; Tupper & Boutilier 1995a). Similar
relations between juvenile fish and sea floor habitat of the northwest Atlantic have been observed for silver hake (Merluccius bilinearis) on amphipod tubes (Auster et al. 1997) and cunner (Tautolagrabus adspersusi on
rocky reefs (Tupper & Boutilier 1997).
Habitat-specific differences in survivorship of post-settlement juvenile cod
have been demonstrated in laboratory experiments (Gotceitas & Brown 1993;
Fraser et al. 1996; Gotceitas et a1.l995; Gotceitas et al. 1997; Lindholm et al.
1999). These studies indicate that associations with the vertical relief provided
by particular physical substrata (e.g. pebble-cobble and boulder fields) and
associated emergent epibionts (e.g. sponges and eelgrass) provide cover
from predation and enhance survival for post-settlement juvenile cod.
Assessment of the ultimate effect of fishing activity on the sea floor and
associated fish communities requires knowledge of the nature and extent of
fishing-induced disturbance and their responses to such disturbance. Alteration of sea floor habitat by fishing activity has been demonstrated for a
number of marine communities around the world (reviewed in Jennings &
Kaiser 1998; Auster & Langton 1999). For example, in the Gulf of Maine,
Auster et al. (996) showed that mobile fishing gear reduces sea floor
habitat complexity through removal of epifauna that provide structure, removal of structure building taxa, and the smoothing of bedforms. On
Georges Bank, the effect of scallop dredging on the gravel pavement of the
northeast peak was quantified, indicating a decrease in the number of
species and species biomass in dredged areas (Collie et al. 1997).
343
tion and ultimate conservation and protection of EFH requires data on fish
population dynamics and the ecological influences of habitat on those dynamics for each life-history stage.
Historically, research on exploited offshore fish populations has been directed toward understanding the dynamics of adults and mortality of
pelagic eggs and larvae (Anderson 1988), whereas the attention of the fisheries management community has focused largely on the management of
adults through traditional controls on fishing effort (e.g . limitations on days
at sea, gear restrictions , and catch quotas) (Sissenwine 1984). Less attention
has been directed to the dynamics of early benthic phase juvenile fish
and the role of habitat in mediating post-settlement processes (e.g. Auster &
Malatesta 1995; Tupper & Boutilier 1995a; Auster et al. 1997) and linkages
between patterns in post-settlement juvenile fish survivorship and the alteration of sea floor habitat by fishing activity (Auster et al. 1996, 1999; Auster
1998;Jennings and Kaiser 1998; Lindholm et al. 1998; Lindholm et al. 1999).
Researchers have observed high densities of settled juvenile cod on the
gravel portion of Georges Bank (Lough et al. 1989), on rocky reefs, sea
grass beds, and gravel of the nearshore environment in Nova Scotia (Tupper & Boutilier 1995 a,b) and over hard bottom in Newfoundland (Gregory
et al. 1997). Although juveniles settle on less complex habitats such as sand,
high post-settlement mortality over habitats with little to no relief lead to
low juvenile survival (Lough et al. 1989; Tupper & Boutilier 1995a). Similar
relations between juvenile fish and sea floor habitat of the northwest Atlantic have been observed for silver hake (Merluccius bilinearis) on amphipod tubes (Auster et al. 1997) and cunner (Tautolagrabus adspersusi on
rocky reefs (Tupper & Boutilier 1997).
Habitat-specific differences in survivorship of post-settlement juvenile cod
have been demonstrated in laboratory experiments (Gotceitas & Brown 1993;
Fraser et al. 1996; Gotceitas et a1.l995; Gotceitas et al. 1997; Lindholm et al.
1999). These studies indicate that associations with the vertical relief provided
by particular physical substrata (e.g. pebble-cobble and boulder fields) and
associated emergent epibionts (e.g. sponges and eelgrass) provide cover
from predation and enhance survival for post-settlement juvenile cod.
Assessment of the ultimate effect of fishing activity on the sea floor and
associated fish communities requires knowledge of the nature and extent of
fishing-induced disturbance and their responses to such disturbance. Alteration of sea floor habitat by fishing activity has been demonstrated for a
number of marine communities around the world (reviewed in Jennings &
Kaiser 1998; Auster & Langton 1999). For example, in the Gulf of Maine,
Auster et al. (996) showed that mobile fishing gear reduces sea floor
habitat complexity through removal of epifauna that provide structure, removal of structure building taxa, and the smoothing of bedforms. On
Georges Bank, the effect of scallop dredging on the gravel pavement of the
northeast peak was quantified, indicating a decrease in the number of
species and species biomass in dredged areas (Collie et al. 1997).