New Model-Based Approach to Accurately Estimate Rare Event Sensitive Species “Bycatch”

I’ll start with a quick note that the Magnuson-Stevens Act does not consider marine mammal entanglements to be “bycatch,” a term which is restricted in the statute to describe fish that are caught and discarded at sea. Instead, marine mammal entanglements incidental to commercial fishing are defined as “takes” which are authorized and permitted in accordance with the Marine Mammal Protection Act. This should explain my heavy use of quotation marks.

The California shark and swordfish drift gillnet (DGN) fishery is one example of a fishery that occasionally entangles marine mammals, but fortunately these unwanted interactions are rare events. Since 1990, the DGN fishery has been required to carry on-board observers to record catch data and over the last 25 years observer coverage levels have hovered around 25%. So how can you accurately estimate annual “bycatch” totals without observing 100% of the trips?

Traditionally, annual “bycatch” totals in the DGN fishery have been generated (or extrapolated) from available observer data using ratio estimates, i.e., 2 sperm whale entanglements were observed in the DGN fishery during the 2010 fishing season with 12% observer coverage, so one could estimate that 16.7 sperm whales were caught that year. Traditional ratio estimates seem pretty fair and straightforward, so what’s the problem?
TIRNOne gigantic problem with traditional ratio estimates is that they often suffer from systematic bias (under-and overestimation of “bycatch”). For example, the most recent sperm whale interaction observed in the DGN fishery prior to the 2 sperm whale interactions in 2010 was back in 1999. Given the historical rarity of sperm whale interactions in the DGN fishery, one could argue that assuming 16.7 sperm whales were actually caught in 2010 while relying solely on traditional data extrapolation is a prime example of overestimating “bycatch.” Furthermore, this particular sperm whale event in 2010 resulted in a temporary DGN fishery area closure and triggered a series of several other reactions and actions from scientists, fisheries managers and NGOs. Bad data is bad for everybody, especially when dealing with endangered species. To this point, Martin et al. (2015) highlights many problems with the estimation and prediction of rare event “bycatch” events combined with low observer coverage in the DGN fishery.

But the good news is that there is a new alternative to annual ratio estimates that result in more stable interannual estimates with better precision called regression tree estimates. But don’t let the negative-sounding name fool you because regression tree estimates are actually very progressive in terms of rethinking the old, traditional, dopey and inaccurate ratio estimator and replacing it with a more probabilistic, model-based estimation approach that moderates inter-annual volatility in “bycatch” estimates. So by all means I urge you to please read, enjoy and share this new paper (the file is over 7mb so give it some time to load):
Carretta, J.V., J.E. Moore, and K.A. Forney. 2017. Regression tree and ratio estimates of marine mammal, sea turtle, and seabird bycatch in the California drift gillnet fishery: 1990-2015. NOAA Technical Memorandum, NOAA-TM-NMFS-SWFSC-568.83p.

sperm_whaleIn the paper you will notice some large differences between annual “bycatch” estimates using regression trees and ratio estimators. For example, the regression tree estimate of sperm whale “bycatch” for the 2010 DGN fishing season was 2.0 whales (2 observed + zero estimated in 433 unobserved sets) compared to a traditional ratio estimate of 16.7 whales. According to the study, given the observed sperm whale “bycatch” rate in the DGN fishery over 26 years (~ 1 animal for every 1,000 sets), it is highly unlikely that observed + unobserved “bycatch” in 2010 was ~ 17 whales. Instead, the study suggests that it is more likely that there were two entanglements, both of which happened to be observed. Like I mentioned before, this serves as a prime example of how ratio estimates can overestimate “bycatch”, but what about underestimations?

According to the study, another problem with traditional annual ratio estimates is that when zero “bycatch” is observed, resulting “bycatch” estimates are zero (with no variance estimate), even if undetected “bycatch” occurs. For example, zero sperm whale entanglements were observed in 648 sets in the first two years of the DGN observer program (1990-1991), when total fishing effort was estimated at over 9,000 sets. Resulting annual ratio estimates of sperm whale “bycatch” in 1990-1991 were zero, which one could be considered an underestimate given the observed long-term “bycatch” rate on 1 whale in every 1,000 sets. In contrast, regression tree “bycatch” estimates for 1990-1991 are approximately 7 sperm whales, which is much more realistic considering the amount of fishing effort.

Progression is good and I can’t stress enough how important it is to have accurate data, which is why I am delighted to share this new study which clearly serves as an example of #OceanOptimism.

Sea Lion Rescue – Mother’s Day 2009

As I mentioned in My Journey, I volunteered as the Assistant Director of the Santa Barbara Marine Mammal Center from 2007-2011. Every weekend and sometimes during the week I was on-call for any and all marine mammal rescues in Santa Barbara County. During those four years or so I estimate that I personally rescued over 1,200 marine mammals, and fortunately over 90% of them were successfully rehabbed and released alive.

But the ones that didn’t make it tend to stand out more in my mind than the ones that did, mainly because I was involved in the euthanization process which is never fun.

This is a video of me rescuing one of the ones who didn’t make it filmed by the man who called it in. She had a rotten burst abscess on her left fore flipper with exposed broken bones that were rotting as well. Amputation was not an option because sea lions swim with their fore flippers. Consequently, this animal was humanely euthanized about 20 minutes after this was filmed. When you see me looking at her wound through the side of the cage at the end of the video, that’s the very moment that I knew we would have to put her down.

The bright side of this tough experience for me was that I was able to get to this animal quickly, before anyone harassed it. In other words, I’m glad that at least it didn’t spend it’s last hours alive suffering any more than it already was.

Your Definition of Bycatch is Most Likely Incorrect

One thing we can all agree on is that bycatch is a very serious problem that threatens healthy fisheries and healthy oceans worldwide. But unfortunately, one thing we cannot seem to agree on is the definition of the word “bycatch” itself. I have come across many concerned citizens, ocean conservationists, and even fishermen who have conflicting definitions of what they think is considered bycatch, which only compounds the seriousness of this complex issue.

So what is your definition and understanding of the word “bycatch?”

What if a longliner who is primarily targeting tuna also caught some “non-target” species such as sharks, swordfish, opah and other marketable fish on the same set and brought it all back to port to be sold to the markets; do you consider these “non-target” species to be bycatch in this tuna fishery? If you answered yes, you are not alone. But unfortunately, according to the Magnuson-Stevens Fishery Conservation and Management Act if you answered yes, you are wrong.


The Definition of Bycatch

The definition of bycatch, as stated in the Magnuson-Stevens Fishery Conservation and Management Act, is:

“Fish which are harvested in a fishery, but which are not sold or kept for personal use, and includes economic discards and regulatory discards. Such term does not include fish released alive under a recreational catch and release fishery management program.”


Because this definition does not include marine mammals, seabirds, and other resources that fall under the National Marine Fisheries Services (NMFS) responsibility, the NMFS uses the following definition of bycatch for its National Bycatch Strategy and bycatch reduction efforts:

“Discarded catch of any living marine resource, plus unobserved mortality due to direct encounter with fishing gear.”


The same rule goes for all U.S. commercial fisheries. While the definition of the word bycatch can vary internationally, any seafood that is brought to port and sold or kept for personal use (such as bait) in any U.S. commercial fishery is not considered to be bycatch according to U.S. Federal law.


Incorrect Definitions of Bycatch

According to The Safina Center at Stony Brook University:

“Bycatch refers to the unwanted sea life people catch when they are fishing for something else.”

According to Oceana’s “Wasted Catch” report:

“Bycatch is the capture of non-target fish and ocean wildlife, including what is brought to port and what is discarded at sea dead or dying.”

So why is this important? One reason it’s important is because when the world’s largest ocean conservation organization does not understand what bycatch even is, then we have a very big problem. When ocean conservation organizations do not understand what bycatch is, it can lead to scientifically flawed statistics published in reports such as “Wasted Catch” which only amplify the confusion by spreading misinformation about responsible U.S. fisheries to the mass general public. I urge you to please read the Regional Fishery Management Council Coordination Committee’s response letter to Oceana’s scientifically flawed “Wasted Catch” report here. As the CCC points out, failure to understand the definition of bycatch severely undermines the many examples of successful bycatch reduction efforts that have been demonstrated by responsible U.S. fisheries to date.

Another reason it is important to understand the true definition of bycatch is that most of the “non-target” species that are mistaken as bycatch by some folks are actually very important components to the economic viability of several responsible U.S. fisheries. More times than not, fishermen rely on catching other marketable species that are not primarily targeted in order to make any kind of profit at all. But economics aside, it’s also important to understand that more and more consumers are demanding local seafood, and non-target species only add to the abundance and diversity of our U.S. seafood choices.


When NGOs and the general public think byctach means one thing, and fisheries managers and scientists know that bycatch means something else, it makes it more difficult for us all to work together to combat this serious problem as a united front. Until we can all agree on what bycatch really means, I’m afraid we may be doing more bad than good for our oceans.


Embracing the Success of Responsible U.S Fisheries Management

Seafood choices used to be simple, as they should be. But over the last twenty years or so we have been bombarded with more information and advice about seafood than ever before and all of a sudden seafood choices started to get very complicated. What used to be a simple choice now requires research on our part, and for some folks the confusion and guilt associated with seafood choices is enough to ruin their appetite, but not me. Complex issues are only as complicated as we allow them to be and when I back up and take a look at the bigger picture, I believe seafood choices are still as simple today as they have ever been. We all have the power to make seafood choices simple again and all it takes is a reevaluation of the issue combined with a little common sense on our part. But before we attempt to make seafood choices simple again, it’s important to recognize what makes seafood choices seem complicated to us to begin with.


eatusseafood_seafoodwatch_mscThe sustainable seafood movement started in the 1990’s and in 1996, the Marine Stewardship Council (MSC) implemented the first certification program. Shortly after, the Monterey Bay Aquarium developed a list of sustainable seafood as part of their 1997-1999 “Fishing for Solutions” exhibit. But I didn’t hear the term “sustainable seafood” until around 2009, and once I did, that’s when seafood choices started to get complicated. Back then I didn’t even know what the word “sustainable” even meant. All of a sudden I found myself hearing about destructive fishing practices, illegal fishing, overfishing, bycatch, and seafood fraud while attempting to reference multiple conflicting seafood sustainability ranking guides in an effort to do the right thing for our oceans. It was quite overwhelming to me at first, but it was super interesting as well.


All of a sudden ocean conservation was on everyone’s radar, but unfortunately I noticed the media was reporting mostly doom-and-gloom news about the state of our fisheries and oceans and not many success stories, while environmental groups were telling us a lot more about destructive fishing practices rather than promoting responsible fisheries. Bad news sells I guess, but instead of focusing on all of the negatives I was hearing about fishing and what not eat, I was hungry to discover and learn more about responsible fisheries as well in an attempt to wrap my head around the bigger picture so that I could better understand this complex issue. As complicated as seafood choices were starting to seem to me, I wanted to make seafood choices simple again and I didn’t want to have to rely on anyone else to make my choices for me.


eatusseafood_sustainable_seafood_cringeLearning about what seafood was considered “sustainable” or not back then was so interesting to me that seafood choices and fisheries research in general ended up turning into an ongoing 6-year “research project” that I am still obsessed with in my spare time to this day. I believe that the introduction of the term “sustainable seafood” is responsible for putting responsible seafood choices on people’s radar for the first time and it also changed my life for the better 6 years ago. But for the last 2 years or so I’ve grown to despise the word “sustainable” to the point that I even cringe every time I hear someone say it, but why?


It’s because I believe the word “sustainable” is now ubiquitous and has completely lost its meaning over the years. Now the word “sustainable” has become a buzz word that’s often used as a marketing tool, but one person or company’s definition of what “sustainable” means to them may be very different than what sustainable means to scientists, or to you. Knowledge is power and when we limit ourselves to only buy what someone else says is “sustainable seafood” when we don’t even know what that term really means anymore, it puts us in a position to where we have no power at all and are forced to rely on seafood guides or eco-labels to tell us what is sustainable or not rather than us being empowered to make well-informed decisions on our own.


Today, 10% of global wild caught seafood comes from fisheries engaged in the MSC certification process, but does that mean that the other 90% of the world’s fisheries are not sustainable? No it does not. In fact, scientists have raised concerns regarding some of the fisheries that are MSC certified. Furthermore, MSC certification can cost as much as $150,000 which limits the certification to only larger-scale fisheries that can afford it while undermining small-scale fisheries that can’t afford it but deserve recognition. But don’t get me wrong because I am not trying to bad mouth the MSC. I’m just saying that I do not think it is wise to live and die by the MSC label when it comes to seafood choices.


That being said, I also do not think it is wise to live and die by seafood guides when it comes to seafood choices. Today there are dozens of seafood advice websites, but like I said before, they often offer conflicting information. Why the conflicting information? A recent article written by Ray Hilborn, professor of aquatic and fishery sciences at the University of Washington states, “Providing seafood advice is now a big business, both with direct payment from retailers to those giving advice, and by fundraising campaigns to “save the oceans” that fail to acknowledge that the existing U.S. fisheries management system provides for sustainability.” With all of the information available at, I’d go as far to say that I would be happy to see seafood advice programs such as Seafood Watch go away for good.


The introduction of the general term “sustainable seafood” may have inspired a new generation of ocean advocates years ago to make more responsible choices, but it seems to have run it’s course and worn out it’s welcome in my opinion. Trying to identify what type of seafood or what gear type is considered “sustainable” was a good starting point for us because it opened our eyes to the issue, but relying solely on the “sustainability” mindset alone as we move forward can be very limiting and often counterproductive in terms of effective ocean conservation. I think it’s unrealistic for us to believe that responsible seafood choices can be defined by a word, a term or a label. The “sustainable seafood” movement is over 20 years old and now I think its time for us to take our seafood choices to the next level.


If we really want to take ocean conservation to the next level, I think we need to stop limiting ourselves by only focusing on what species and gear types that people tell us are “sustainable,” and start to use our own brains by thinking more in terms of identifying and purchasing seafood that we know is responsibly sourced from nations with responsible fisheries management. eatusseafood_ditch_sustainableBy taking a step back, looking at the bigger picture, focusing on what facts I did know and reevaluating what was important to me, all of a sudden seafood choices started to seem simple again. I am not going to try to tell you what to think or do, but for me personally, I arrived at the conclusion that buying seafood that is harvested in the U.S. and supporting U.S. fisheries is the most responsible and effective action we can take to support responsible fisheries, healthy oceans and coastal communities.


One fact that has always been a huge concern of mine is that up to 90% of the seafood consumed in the U.S is imported. This is up from 67% just 12 years ago creating an annual trade deficit of more than $10.4 billion, which is second only to oil in the natural resources category. What also scares me is that only about 2% of imported seafood is inspected at all, only 1% is inspected for mislabeling, and only .1% is tested for banned drug residues.


It doesn’t take much research to realize that some foreign fisheries are either poorly managed or not managed at all. We hear a lot about illegal, unreported, and unregulated (IUU) fishing, which is a big problem in other countries but not here in the U.S. We hear that 33% of seafood tested in American restaurants is mislabeled, but our domestic fisheries follow seafood-labeling rules. We hear a lot about overfishing, but the U.S has essentially eliminated overfishing, with only 9% of stocks now fished at rates higher than would produce long-term maximum yield.


There are a lot of concerns surrounding what little we know about foreign fisheries, but we do know that the U.S has one of the lowest levels of overfished stocks and 40 years of evidence (the Magnuson-Stevens Act) to back it up. It seems obvious to me that supporting U.S. fisheries is an easy way to simplify responsible seafood choices, so why aren’t NGOs promoting this message? eatusseafood_ray_hilbornAccording to Ray Hilborn, “Some NGOs now gain so much revenue from companies that sell seafood and concerned citizens, that they simply cannot admit the U.S. success.” When we ignore the success of responsible U.S. fisheries management while imports continue to increase, we are essentially rewarding the “bad guys” while punishing the “good guys.” Meanwhile, the number of commercial fishermen in California has decreased over 75% in the last 30 years.


I’ve noticed that other folks are starting to arrive at the same conclusion that I have, and fortunately it is becoming easier and easier for us to buy U.S. seafood. The first community supported fishery (CSF) was started in Port Clyde, Maine, in 2007 but today there are 187 locations in North America. If you want delicious canned albacore tuna that is caught pole-and-line one at a time right here in the U.S. all you have to do is visit your local Whole Foods or you can simply order it online. Even Costco offers several U.S. seafood options. No matter where you live it is now easier than ever to buy U.S. seafood, and I sure wish that more folks would.