Here are the nuts and bolts of the studies for those who don't want to go to the link and read the whole thing
Impact of catch and release
This study demonstrated that C&R salmon represented
20% of the multi-sea-winter population and were one
of the parents for 22% of the genotyped offspring,
hence playing an important role in the reproductive
output of the whole population. Our results thus con-
firm the role played by released salmon in the observed
higher redd and parr density that followed the inception
of C&R fishing on the Ponoi River in Russia and
on the Alta River in Norway (Whoriskey et al. 2000;
Thorstad et al. 2003). Thus, C&R is an effective conservation
and management tool towards maintaining the
socio-economic benefits from recreational fishing while
ensuring a minimal impact on the exploited population,
pending appropriate practices (see below). In Canada,
annual economic value for wild Atlantic salmon has
been estimated at $255 million and 3872 full-time
equivalent jobs are directly created annually because of
wild Atlantic salmon, most of which (86%) are related
to recreational fishing (ASF 2011). Furthermore, in this
study, as well as in other previous studies (Whoriskey
et al. 2000; Thorstad et al. 2003), a small proportion
(namely, 5%, 11% and 4%) of salmon were caught and
released more than once in the fishing season, thus
increasing the value of each fish and the economic
benefits of C&R.
At an individual scale, if we exclude from the analysis
the five C&R salmon that did not pass through the
fish ladder, C&R salmon had the same probability of
reproduction as noncaught salmon. On the other hand,
when taking the fish that did not pass the ladder into
account, C&R impaired access to reproduction of multisea-winter
salmon, reducing their chances of mating by
12%. Several reasons may explain why these salmon
never crossed the dam. Indeed, although all except one
were reported to be in excellent condition, these salmon
could have died or aborted migration as a result of
C&R. However, these salmon could also have come in
the first pools of the river as visitors before returning to
the sea. This is plausible based on migrant detection in
other Atlantic salmon studies (Jonsson et al. 2003; Dionne
et al. 2008). Based on the previous studies and on
the fact that we do not have data on the behaviour of
noncaught salmon in those downstream pools, we then
suggest that C&R does not significantly impair the
access to reproduction of large salmon.
Within the group of large salmon for which at least
one offspring was assigned, C&R had a significant,
albeit weak, impact on the number of offspring inferred
and that effect was dependent on fish length. Thus,
while smaller fish fitness did not seem to be impaired
by C&R, larger C&R salmon produced significantly less
offspring than same size noncaught salmon. Previous
studies of the effect of size on salmonids post-release
mortality have led to mixed conclusions (Bartholomew
& Bohnsack 2005). However, size has been identified as
an important source of variability to the physiological
disturbance of rainbow trout captured by angling as
larger fish showed higher level of plasma cortisol, glucose
and lactate levels (Meka & McCormick 2005). In
Atlantic salmon, angled salmon showed decreased
plasma concentration of calcium and pH and a higher
plasma concentration of glucose, lactate, osmolarity,
chloride and sodium than nonangled fish and the magnitude
of the disequilibrium for plasma concentration
of calcium, lactate and pH was positively correlated
with body length (Thorstad et al. 2003). Larger fish take
longer to land and that could explain why they suffer
more important physiological disturbance and reduced
fitness from C&R (Thorstad et al. 2003; Meka 2004).
Fishermen should thus minimize the time elapsed
between hooking and landing to minimize the impact
of C&R.
Water temperature has been identified as a major predictor
of salmonid survival rate (Muoneke & Childress
1994; Thorstad et al. 2003; Boyd et al. 2010), explaining
72% of the variation in survival from Atlantic salmon
C&R angling (Dempson et al. 2002). Air exposure is also
associated with C&R-related physiological disturbance
(Ferguson & Tufts 1992; Schreer et al. 2005), and studies
recently showed that there are interactive effects of air
exposure duration and water temperature on survival
and physiological disturbances of C&R fish (Gingerich
et al. 2007; Gale et al. 2011). Here, water temperature
negatively impacted reproductive success of salmon
kept in the water, but in the temperature range of
12–17 °C, air exposure time had a greater negative
impact on fitness than water temperature. Depending
on the temperature, reproductive success can be up to
two or three times higher for salmon kept in the water
compared with those exposed to air for 10 s and with
those exposed to air for >10 s, respectively. Predictions
obtained for water temperature above 17 °C, where a
longer air exposure seems beneficial in terms of fitness,
as well as the positive relation between water temperature
and the number of produced offspring for the long
exposure time group, could be explained by the fact
that high water temperatures may enhance the recovery
of exercised Atlantic salmon (Wilkie et al. 1997). Thus,
the conditions in which C&R is conducted influence the
success of the practice in terms of conservation. Consequently,
precaution must be taken to limit C&R in
warm water periods and avoid air exposure prior to
release.
Overall, this study measured the impact of C&R on
individual reproductive success and allowed an evaluation
of its sustainability for an exploited fish population.
Nevertheless, our study suffers from limitations that
should be considered to improve further studies of this
type. First, ideally such studies should include more
than 1 year of data because other similar studies
showed that patterns of reproductive success and selection
gradients can change substantially from year to
year (Ford et al. 2008). Secondly, reproductive success
was evaluated at the fry stage only, and consequently,
comparison of the production of offspring that survive
to reproduce would be warranted in future studies.
Finally, there is a need to perform similar studies in
other populations to bring stronger support to our statements
about the general merits of this management
strategy.