364 
Abstract — Catch rates from surveys 
are used as indices of abundance for 
many fish species. Relative abundance 
estimates from surveys with longline 
gear do not usually account for pos- 
sible effects of gear saturation, which 
potentially creates competition among 
fish for baited hooks and misrepre- 
sentations of abundance trends. We 
examined correlations between catch 
rates of sablefish (Anoplopoma fim- 
bria) and giant grenadier ( Albatros - 
sia pectoralis ) and between sablefish 
and shortraker ( Sebastes borealis) and 
rougheye rockfish (Sebastes aleutia- 
nus) from 25 years of longline sur- 
veys in Alaska waters for evidence 
of competition for hooks. Sablefish 
catch rates were negatively correlated 
with giant grenadier catch rates in 
all management areas in Alaskan 
waters, and sablefish and rockfish 
were negatively correlated in five of 
the six areas, indicating that there 
is likely competition for hooks during 
longline surveys. Comparative analy- 
ses were done for trawl survey catch 
rates, and no negative correlations 
were observed, indicating that the 
negative correlations on the longline 
surveys are not due to differing habi- 
tat preferences or direct competition. 
Available adjustments for gear satura- 
tion may be biased if the probability 
of capture does not decrease linearly 
with baited hooks. A better under- 
standing of each fish species’ catch 
probabilities on longline gear are 
needed before adjustments for hook 
competition can be made. 
Manuscript submitted 10 January 2008. 
Manuscript accepted 10 June 2008. 
Fish. Bull. 106:364-374 (2008). 
The views and opinions expressed or 
implied in this article are those of the 
author and do not necessarily reflect 
the position of the National Marine 
Fisheries Service, NOAA. 
Evidence of hook competition 
in longline surveys 
Cara J. Rodgvefler (contact author) 
Chris R. Lunsford 
Jeffrey T. Fujioka 
Email address for C. J. Rodgveller: Cara.Rodgveller@noaa.gov 
National Oceanic and Atmospheric Administration 
National Marine Fisheries Service 
Alaska Fisheries Science Center 
Auke Bay Laboratories 
17109 Point Lena Loop Road 
Juneau, Alaska 99801 
Catches from longline surveys are 
used to estimate relative fish abun- 
dance for many benthic and pelagic 
fish species around the world, includ- 
ing: sablefish ( Anoplopoma fimbria, 
Hanselman et ah, 2006), Pacific hali- 
but (Hippoglossus stenolepsis, Clark 
and Hare, 2006), Greenland halibut 
( Reinhardtius hippoglossoides, Woll 
et al., 2001; Murua and Cardenas, 
2005), sharks (class Elasmobranchia, 
e.g., Musick et al., 1993; Kohler et 
al., 1998; Simfendorfer et al., 2002), 
red snapper ( Lutjanus campechanus) 
and yellowedge grouper ( Epinephelus 
flavolimbatus) (Cook, 2007), rough- 
head grenadier ( Macrourus berglax, 
Murua and Cardenas, 2005), and 
many demersal fish species off the 
Azores Archipelago in the mid-Atlan- 
tic (Menezes et al., 2006). In these 
surveys, it is assumed that catch rate 
is proportional to abundance, and the 
probability of catching a fish remains 
constant even as the number of baited 
hooks decreases. However, several 
factors may affect this relationship. 
Water temperature (Sogard and Olla, 
1998a, 1998b; Stoner and Strum, 
2004) and feeding history (Lpkkeborg 
et al., 1995; Stoner and Strum, 2004) 
affect the activity level and feeding 
behavior of sablefish. The area and 
strength of the scent plume surround- 
ing bait can also affect the probabil- 
ity of capturing a fish (Lpkkeborg et 
al., 1995). Additionally, in some cases 
longline gear may become saturated 
with fish, which potentially creates 
competition among fish for baited 
hooks (Murphy, 1960; Rothschild, 
1967). Hook competition may reduce 
the probability of catching a fish as 
the number of baited hooks decrease, 
and factors such as temperature and 
feeding behavior may affect the rate 
of gear saturation and the intensity of 
competition for baited hooks. 
The National Marine Fisheries 
Service (NMFS) Alaska Fisheries 
Science Center (AFSC) conducts an- 
nual longline surveys to estimate the 
relative abundance of major ground- 
fish species in the eastern Bering 
Sea, Aleutian Islands, and the Gulf 
of Alaska (Sigler, 2000). The sur- 
vey is primarily designed to assess 
sablefish and indices of abundance 
have been computed since 1979. Re- 
cently, catch rates of other ground- 
fish species, such as giant grenadier 
( Aibatrossia pectoralis) (hereafter 
grenadier), and shortraker (Sebastes 
borealis, Clausen, 2006a, 2006b) and 
rougheye rockfish ( Sebastes aleutia- 
nus, Shotwell et al., 2006), have also 
been used to assess population lev- 
els. Sablefish are the dominant spe- 
cies caught on the longline surveys 
and most reside in the -200-1000 m 
depth range (Sigler, 2000). Sablefish 
depth range overlaps those of the 
grenadier (>300 m) and shortraker 
and rougheye rockfish (-250-500 m), 
indicating that these species could po- 
tentially be competing with sablefish 
for longline hooks. Also, experimen- 
tal evidence indicates that sablefish 
are adept at finding baited hooks on 
the longline surveys, even when few 
