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Fishery Bulletin 106(4) 
Figure 5 
Scatterplots of catch rates from the National Oceanic and Atmospheric Administration 
Alaska Fisheries Science Center Gulf of Alaska longline and trawl surveys (1984, 1987, 
1990, 1993, 1996, 1999, 2001, 2003, and 2005). (A) Plot of grenadier (giant grenadier 
[Albatrossia pectoralis ]) and sablefish ( Anoplopoma fimbria) catch rates on longline 
gear; (B) rockfish (shortraker [ Sebastes borealis] and rougheye [Sebastes aleutianus] 
rockfish) and sablefish catch rates on longline gear; (C) catch rates of grenadier and 
sablefish from the trawl surveys; (D) rockfish and sablefish catch rates from the trawl 
surveys. Ninety percent density ellipses are included to demonstrate the trend. Catch 
per unit of effort is abbreviated as CPUE. Data transformations are also abbreviated: 
square root (SQRT), fourth root (4 th rt), and natural logarithm (LN). 
Effects of competition on grenadier and rockfish catch 
rates will vary by area because of spatial abundance dif- 
ferences of these species and other groundfish. Negative 
correlations between sablefish and grenadier catch rates 
on longline gear varied with the density of sablefish, 
and the strongest negative relationships were found in 
the West Yakutat area and East Yakutat and Southeast 
area where sablefish catch rates and abundances were 
highest (Hanselman et al., 2006). Negative correlations 
between sablefish and rockfish catch rates were weaker 
than the correlations between sablefish and grenadier 
catch rates. Correlations between sablefish and rockfish 
catch rates were likely weaker because there were a 
variety of species caught in relatively large numbers 
in rockfish preferred depths, such as Pacific halibut 
(Hippoglossus stenolepsis), arrowtooth flounder (Ather- 
esthes stomias), and Pacific cod ( Gadus macrocephalus) . 
In areas where there were many other species caught 
at preferred rockfish depths (Aleutian Islands, West- 
ern Gulf, and Central Gulf areas), the relationship 
between sablefish and rockfish catch rates was weaker 
than in other areas. Hence, sablefish and rockfish may 
compete with multiple species for hooks at rockfish pre- 
ferred depths and dampen the direct competition with 
each other. The negative correlations at specific depths 
where grenadier or rockfish catch rates were highest 
were even greater than the negative correlations of the 
entire preferred depth ranges. This finding also shows 
that hook competition will vary depending on the depth, 
area, and possibly the abundance of the species of inter- 
est as well as other species. 
As our data and data from other studies indicate, 
aggressive predators may out-compete other species for 
hooks on longline gear (e.g., Skud, 1978; Zenger and Si- 
gler, 1992). For example, the proportion of Pacific hali- 
but caught increased as hook spacing increased because 
when hooks were widely spaced and less abundant, 
Pacific halibut out-competed other species for baited 
hooks (Skud 1978). This experiment also indicates that 
halibut are caught in proportion to their abundance, 
while other less aggressive species may not be. Simi- 
larly, Zenger and Sigler (1992) and Sigler and Zenger 
(1994) reported that catches of shortspine thornyhead 
( Sebastolobus alascanus) and grenadier were low in 
