Weaver et at: Influence of nutrients from carcasses of Petromyzon marinus on growth of larval conspecifics 
149 
changes in population dynamics, including the recovery 
or re-establishment of fish populations (e.g., salmonids; 
Vincenzi et ah, 2012). 
We assumed that the addition of nutrients from 
mortality of postspawning adult sea lamprey (i.e., 
changes in productivity) influences the variability as¬ 
sociated with growth and metamorphosis of larval sea 
lamprey. In reality, larval metamorphosis is dependent 
upon many different biological factors (e.g., lipid accru¬ 
al; Lowe et ah, 1973) and variation in environmental 
conditions that extend beyond productivity alone. Some 
of these factors have been thoroughly explored among 
other anadromous fish, especially salmonids, and may 
have implications for population demographics and per¬ 
sistence of sea lamprey. Anadromous salmon parr, for 
example, grow in freshwater before becoming smolts, 
a process characterized by a series of energetically de¬ 
manding physical and physiological changes (McCor¬ 
mick et ah, 1997). Research has shoen that higher wa¬ 
ter temperatures provide parr with more opportunities 
for growth, up to an optimal temperature after which 
growth is likely reduced, and this growth may result in 
earlier smoltification (Zaugg and McLain, 1976; Thorpe 
et al., 1989). Nutrients from carcasses of sea lamprey 
stimulate productivity during spring, a critical period 
of temperature-driven increases in metabolism for fish 
facing potential limitations in resources (Hall, 1972; 
Weaver et al., 2015; Weaver et al., 2016). Therefore, 
salmon parr that are subsidized directly and indirectly 
by these resources may benefit from a compensatory 
growth as fish approach the smolt stage (Guyette et ah, 
2013; Sigourney et ah, 2013). This enhanced growth 
could potentially increase survival and reduce the 
number of years spent in freshwater before the young 
salmon successfully migrate to the ocean (Horton et 
ah, 2009). Weaver (2017) showed nutrient assimilation 
of carcasses of adult sea lamprey by larval conspecif¬ 
ics, but because it has not yet been documented that 
carcasses contribute to larval growth, this process re¬ 
mains an important area for future study. 
Many of the parameters used in our model are poorly 
documented in the scientific literature. Our model run 
for the unsubsidized, stabilized population was sensi¬ 
tive to several life-history and recruitment parameters. 
We used a sensitivity analysis to bracket what would 
be realistic values, with age-1 mortality being the 
most sensitive parameter among the tested variables. 
Population dynamics are largely governed by 3 demo¬ 
graphic processes: recruitment, growth, and mortality 
(Hilborn and Walters, 1992), and results from our sen¬ 
sitivity analysis indicate that small changes in these 
processes can have substantial effects on both recruit¬ 
ment and the returning populations of spawning sea 
lamprey. Furthermore, the short-term dynamics of the 
model output are driven by the assumptions with us¬ 
ing the Ricker curve, which may or may not accurately 
reflect the biology of sea lamprey. Other recruitment 
curves (e.g., the Beverton-Holt) may be biologically 
more realistic, but the long-term dynamics and stable 
states achieved do not differ. The results of our model¬ 
ing highlight the need for more detailed life-history in¬ 
formation for anadromous fish species like sea lamprey. 
Anadromous sea lamprey are native to Atlantic 
coastal waters and are an important driver of nutri¬ 
ent cycling (Weaver et ah, 2016). However, sea lamprey 
have garnered notoriety from their invasion into the 
Laurentian Great Lakes and their contribution to the 
decimation of native fish populations and altered food 
webs (Applegate, 1950; Bronte et al., 2003; Ricciardi, 
2006; Great Lakes Fishery Commission 8 ). Anadromous 
and landlocked populations exhibit similar life-history 
strategies, but the ecological implications have invoked 
differing fisheries management actions. Our model¬ 
ing exercise was framed in the context of conserving 
anadromous Atlantic coastal populations, but these 
results may also have important implications for the 
way in which sea lamprey are managed in other sys¬ 
tems. Sea lamprey in the landlocked Great Lakes are 
managed as a pest species, and recruitment dynam¬ 
ics may be influenced by the types of eradication and 
control methods used (Jones, 2007; Dawson and Jones, 
2009). However, generally speaking, managers attempt 
to control invasive species with limited knowledge of 
their life history (Simberloff, 2003). A more complete 
understanding of the population dynamics of a species 
is critical for both population conservation and control 
strategies (Great Lakes Fishery Commission 8 ). Our 
model is based on the hypothesis that nutrients from 
carcasses of sea lamprey increase larval growth rates 
and enhance earlier metamorphosis. This hypothesis is 
consistent with research in the Great Lakes, indicat¬ 
ing that more productive waters contain faster growing 
larvae that reach metamorphosis at younger ages (Pur¬ 
vis, 1980; Morkert et al., 1998; Griffiths et al., 2001). 
Therefore, predictive models used for management and 
control measures of larval sea lamprey (Treble et al., 
2008) may be more accurate with the incorporation of 
demographic shifts in populations of sea lamprey. The 
results from our model indicate the consequences of 
potential feedback mechanisms that may be relevant 
to decisions regarding management actions to conserve 
and restore ecosystem functions or control and eradi¬ 
cate an invasive species. 
Currently, the focus of natural resource management 
has shifted toward ecosystem restoration (Palmer et 
ah, 2014). Our model closes the hypothesized nutrient 
loop, and results from our model indicate a feedback 
process by which nutrients from carcasses of sea lam¬ 
prey influence spawning stocks by subsidizing growth 
that may improve larval fitness (Hall, 1972; Hall et 
ah, 1992). Globally, many anadromous fish species are 
threatened or imperiled (Limburg and Waldman, 2009) 
and our results indicate that current management 
strategies may need to consider energy and nutrient 
exchanges between ecosystems and the effects of these 
Great Lakes Fishery Commission. 2011. Strategic vision 
of the Great Lakes Fishery Commission 2011-2020. Great 
Lakes Fish. Comm., Misc. Publ. 2011-13, 29 p. [Available 
from website.] 
