Stevenson et al.: Interactions between fisheries and early life stages of skates in nursery areas of the Bering Sea 
13 
cies (Alaska skate) and one gear type (longline), over 
half of the egg cases were assessed as viable. For all 
other species and gear types, the proportion of egg 
cases that were viable was no more than 30%. This 
discrepancy may indicate that more fishing activity 
is occurring near the central portion of nursery areas 
used by Alaska skate than near those used by other 
species and that longline vessels are fishing closer to 
these areas than trawlers. 
Hoff (2010) found that skate nursery areas gener¬ 
ally consist of small areas with a high percentage of vi¬ 
able eggs surrounded by larger areas of predominantly 
(>70%) empty egg cases; therefore, fishing activity near 
these high-density areas of nursery sites lead to inter¬ 
actions with higher proportions of viable eggs. How¬ 
ever, this difference in viability proportion among gear 
types may be at least partially due to sampling arti¬ 
facts. Egg cases captured in trawls may be subjected 
to very different forces than egg cases pulled up on 
a longline. Skate embryos can be expelled from their 
egg cases during capture and gear retrieval, and it can 
be difficult to determine whether a particular egg case 
was empty when encountered by the fishing gear or it 
had an embryo that was squeezed out at some point 
between capture and assessment. Therefore, without 
additional information on the relative expulsion rate 
of skate embryos from egg cases captured in different 
gear types, it is difficult to interpret the differences in 
viability rates presented here for egg cases captured 
with different gear types. 
For viable egg cases, the mortality rate of skate 
embryos brought to the surface by fishing gear is un¬ 
known. In fact, discard mortality even for adult skates 
is not well known, although recent studies have begun 
to examine at least the short-term mortality of skate 
bycatch (see review by Ellis et al., 2017). Skate embry¬ 
os of viable egg cases caught in fishing gear may suffer 
increased mortality for a number of reasons, including 
hook puncture, thermal stress, barotrauma, and crush¬ 
ing and concussive stress. Even if they are not injured 
directly, discarded egg cases may be displaced sever¬ 
al kilometers or more from the nursery area, leaving 
them more vulnerable to predation and possibly expos¬ 
ing them to environmental conditions that are develop- 
mentally suboptimal or even lethal. 
The majority of egg cases identified for this study 
were encountered near documented skate nursery 
areas, particularly the nursery areas designated as 
HAPC. Egg case densities at these sites can be as 
high as 800,000 eggs/km 2 (Hoff, 2008, 2010), and nurs¬ 
ery areas cover several square kilometers of seafloor. 
Therefore, fishing operations conducted near these 
sites are expected to encounter high concentrations of 
egg cases. Concentrations of egg cases for Alaska skate 
were reported in 2 additional areas well away from all 
nursery areas designated as HAPC. One of these ar¬ 
eas of concentration, in the southern part of Zhemchug 
Canyon, is near a known nursery area for Alaska skate 
that has not been designated as an HPAC (Rooper et 
al., in press), likely explaining the abundance of egg 
cases in that area. The other area of concentration, in 
the northwestern part of Pribilof Canyon, is not near 
any known nursery area for Alaska skate, although 2 
nursery areas for other species ( B. minispinosa and the 
deepsea skate) are known in this area (Rooper et al., 
in press). This area of concentration of egg cases may 
indicate the presence of an additional nursery area for 
Alaska skate that has not yet been documented. 
The overall number of egg cases reported by observ¬ 
ers, and the locations of those encounters, indicate that 
fishing gear is being deployed in and around skate 
nursery areas, including those designated as HAPC. 
Clearly, skate embryos of viable egg cases caught in 
fishing gear are exposed to increased mortality rates. 
However, fishing activities have a variety of both short- 
and long-term effects on benthic marine communities 
(Auster et al., 1996; Auster and Langton, 1999), includ¬ 
ing the disturbance and redistribution of sediments 
and benthic organisms as well as the outright physical 
impacts on organisms contacted, but not captured by, 
fishing gear. In addition, although some types of ben¬ 
thic habitat are more vulnerable than others and some 
types of fishing gear are more damaging than others 
(Grabowski et al., 2014; Hiddink et al., 2017), the ef¬ 
fects of any fishing gear on skate nursery areas have 
not been assessed. Therefore, fishing activity may be 
causing additional mortality to embryos not recorded 
in catch statistics, and the overall effects of fishery in¬ 
teractions with skate egg cases and nursery areas are 
still largely unknown. 
Skate populations in the EBS appear to be healthy, 
and their overall biomass has been stable over the 
past 30 years (Hoff, 2006; Ormseth, 2017). However, 
significant community shifts in skate assemblages are 
not necessarily accompanied by declines in overall bio¬ 
mass (Dulvy et al., 2000; Stevens et al., 2000), and the 
slow growth and low reproductive potential exhibited 
by most skates (Ebert, 2005; Ebert et al., 2008) make 
them particularly vulnerable to environmental distur¬ 
bance. Therefore, a cautious approach to the manage¬ 
ment and conservation of skate species is warranted. 
Previous work has documented the prevalence of adult 
skates commonly caught as bycatch in commercial 
fisheries (Stevenson and Lewis, 2010), and this study 
documents the interactions of fisheries with the early 
life history stages of skates and their nursery habitats. 
The mortality associated with fishing activities and the 
long-term effects of fishing pressure on the skate popu¬ 
lations of the EBS are difficult to quantify. However, 
the potential for fishing activities to have significant 
detrimental effects on skate species exists, and this 
study emphasizes the need to continue monitoring 
these interactions, both with adults and with skates in 
early life history stages. 
Acknowledgments 
This research was supported by grant no. 1404 from 
the North Pacific Research Board. We thank the ob- 
