Abstract
Intense fishing pressure and
climate change are major threats to fish population and coastal
fisheries. Larimichthys crocea (large yellow croaker) is a
long-lived fish, which performs seasonal migrations from its spawning
and nursery grounds along the coast of the East China Sea (ECS) to
overwintering grounds offshore. This study used length-based analysis
and habitat suitability index (HSI) model to evaluate current
life-history parameters and overwintering habitat suitability ofL. crocea , respectively. We
compared recent (2019) and historical (1971-1982) life-history
parameters and overwintering HSI to analyze the fishing pressure and
climate change effects on the overall population and overwintering phase
of L. crocea . The
length-based analysis indicated serious overfishing of L. crocea ,
characterized by reduced catch, size truncation, constrained
distribution, and advanced maturation causing a recruitment bottleneck.
The overwintering HSI modeling results indicated that climate change has
led to decreased sea surface temperature during L. croceaoverwintering phase over the last half-century, which in turn led to
area decrease and an offshore-oriented shifting of optimal overwintering
habitat of L. crocea . The fishing-caused size truncation may have
constrained the migratory ability and distribution of L. croceasubsequently led to the mismatch of the optimal overwintering habitat
against climate change background, namely habitat bottleneck. Hence,
while heavily fishing was the major cause of L. crocea collapse,
climate-induced overwintering habitat suitability may have intensified
the fishery collapse of L. crocea population. It is important for
management to take both overfishing and climate change issues into
consideration when developing stock enhancement activities and policy
regulations, particularly for migratory long-lived fish that share a
similar life history to L. crocea . Combined with China’s current
restocking and stock enhancement initiatives, we propose recommendations
for future restocking of L. crocea in China.
Key words: Larimichthys crocea, overfishing, climate
change, length-based analysis, HSI model, East China Sea.
INTRODUCTION
Globally, heavily fishing activities and climate change are rapidly
reducing the abundance of many marine organisms and increasing the
likelihood of species extinction (Hoegh-Guldberg and Bruno 2010, Cinner
et al. 2012, Burgess et al. 2013, Payne et al. 2016). For instances,
intensive fishing and climate change have caused overfishing and
declined catches in Canada, Iceland, and China (Pauly et al. 2011, Du et
al. 2014, Liang and Pauly 2017). Previous studies showed that fishing
pressures and climate change can affect the (i) the life-history
strategy of individuals, via impacts on physiology, morphology and
behavior (Ba et al. 2016, Olafsdottir et al. 2016); (ii) the population
dynamics, via changes to key population processes throughout an
organism’s life-history and habitat suitability (Perry et al. 2005).
Hence, bottlenecks of any life-history stage (e.g. spawning, hatching,
larval survival, recruitment settlement, growth, and adult survival),
and habitat suitability can cause overfishing of exploited species. In
this context, recruitment bottleneck and habitat bottleneck are most
well documented (Almany and Webster 2006, Caddy 2011). Correspondingly,
the potential cause of overfishing is mismanagement because of a poor
understanding of recruitment bottleneck and habitat bottleneck that
constrain the productivity of the overall population.
Fishing alters the size structure by removing large fish exacerbated by
size-selective gear. Heavily fishing can diminish the ability of fish to
reproduce (recruitment overfishing) and/or constrain the overall
recruitment ability before they can fully realize their growth potential
(growth overfishing) (Diekert 2012) via size truncation effect (STE)
(Berkeley et al. 2004, Ottersen et al. 2006, Froese et al. 2008,
Langangen et al. 2019). This effect states that population shifts with
decreasing body sizes and advancing maturation characteristic of the
life-history changes induced by fishing (Berkeley et al. 2004, Anderson
et al. 2008, Bell et al. 2015). Hence, fishing for juveniles and
mega-spawner can weaken the reproductive potential of a fish stock,
called ‘recruitment bottleneck’ (Doherty et al. 2004). Such bottlenecks
are visible in long-term time series and are a common cause of collapse
in intense fished stocks, for example in Western cod, Pacific rockfish
and North Sea ground fish (Harvey et al. 2006, Poulsen et al. 2007,
Froese et al. 2008).
Climate change-caused environmental conditions shift can have negative
effects on fish population (Graham et al. 2011, Johnson et al. 2011). In
general, species’ distribution patterns are relative with both
life-history strategies (Anderson et al. 2013) and physiology tolerance
on environmental variables, such as sea surface temperature (SST),
chlorophyll-a concentration (Chl-a), sea surface salinity (SSS),
currents et al. (Guan et al. 2013, Yu and Chen 2018). Environmental
shift can selectively affect the habitat suitability of target species
(Farrell et al. 2008). Lower habitat suitability of any life-history
stage can lead to species-specific ‘habitat bottleneck’ and latter can
have large consequences for lose several fish’s climatically suitable
habitat, for examples, Norwegian herring, Maine cod and Mid-Atlantic
Bight winter flounder (Bell et al. 2015, Pershing et al. 2015).
Heavily fishing activities and shift in environmental conditions can
have combined effects on fishery collapse, especially for long-lived
species (Rose 2004, Hsieh et al. 2009, Gascuel et al. 2014).
Specifically, some studies suggested that long-lived species are
expected to have slower demographic response to climate change (Berteaux
et al. 2004, Wilson et al. 2010). Additionally, fishing-caused STE can
exacerbate long-lived fish degradation via diminishing ‘bet-hedging’
capacity, including the ability to migrate and avoid poor areas, having
flexibility in spawning times and locations, and production of
high-quality offspring that survive in a broader suite of environmental
conditions, for adapting to rapid climate change (Bell et al. 2015).
However, no example exists that demonstrate the STE and the
climate-induced effects on long-lived migratory fish in the most heavily
fishing (and minimally managed) marine ecosystem in the world: the East
China Sea (ECS) (Szuwalski et al. 2017). To fill the knowledge gaps, we
require a species that: first, under intensive fishing pressure; second,
has specific habitat requirements; third, the habitat of which is
affected by rapid climate-induced habitat suitability variation; fourth,
has been reliably assessed over a long period by field surveys.
In the following, we provide an appropriate example by discussing
changes in specific population dynamic of
an overexploited, long-lived,
migratory fish in the ECS, the large yellow croaker (Larimichthys
crocea ). The collapse of L. crocea represents an
interesting example to explore both heavily fishing and climate change
on overall population: first, L. crocea ranked top among the four
major marine economical fishes in China in last century (Zhang et al.
2010) but suffered collapse since the 1980s. The latest International
Union for Conservation of Nature (IUCN) Red List of Threatened Species
labelled L.croce s as ‘critically endangered (CR)’ (Liu et al.
2020).Second, L. crocea is a long-lived species with maximum age
21 years in 1960s (Zhang et al. 2017). Accompanied by population
collapse, the L. crocea population in the ECS is characterized by
decreased maximum age and body size, and advanced maturation (Ye et al.
2012). Third, L. crocea is a migratory fish which conduct
climatic migrations (e.g. movements driven by physiological tolerances
of individuals to environmental factors such as temperature or salinity)
and gametic migrations (e.g. movements that increase reproductive
success of individuals by promoting gonad development, increasing sexual
encounter rates, or increasing the survival of offspring) between
offshore water and coastal water during autumn-winter and spring-summer
respectively (Fig. 1A).